Louis A. Kamenka 2015-05-05 00:16:58
The first in a series of articles that explore the properties of the various stone groups to explain the importance of this knowledge in selecting the most appropriate stone for specific building and construction applications ABSTRACT This series of articles will focus primarily with the geological aspects of the three major groups of natural stone that have been identified by geologists — Sedimentary, Igneous and Metamorphic rocks — and will assist architects, quarriers, manufacturers and distributors primarily in building, construction, masonry and landscaping projects to develop a better understanding of the unique and enduring values of natural stone. With this knowledge, we can proceed to identify and understand some of the more significant properties of natural stone within each broad rock classification to then assign them names. Ideally, this information will aid in finding a common nomenclature that will be useful to all persons involved in the building, quarrying, marketing, planning and usage of these natural products. The geologic knowledge provided will emphasize the benefits of natural stone and provide answers to some key questions that many people have concerning natural stone and its applications. INTRODUCTION As mentioned, all rocks found at the Earth’s surface fall into three categories — Sedimentary, Igneous and Metamorphic — with an additional insignificant sprinkling of approximately 60 tons of stardust/meteorites added daily to the total exterior of our Planet. The distribution of these rock types varies from place to place as the earth’s crust is constantly changing due to largescale processes constantly taking place.Processes such as plate tectonic activity, the movement of large landmasses where new crustal rocks are being formed and older rocks consumed — together with the constant active processes of physical and chemical weathering of rock — continually reshape the earth’s surface and alter the rocks and minerals being exposed to the various forms of weathering. Earth scientists agree that we do not have one single sample of rock that has remained unchanged since the earth formed, or at least we haven’t found it yet. If the earth’s surface was not constantly moving and being subjected to weathering processes, it would probably have an appearance more similar to that of a Moon or Mars landscape. Earth’s geology is a very large topic, and at first glance, may seem to be an overwhelming task to understand and identify. The approach to this series of articles is an opportunity to share general knowledge of rocks and minerals origins and their identification. Ideally, the reader will find a starting point on which to launch their understanding and appreciation of our wonderful natural resource. For our industry, the article intends to provide a deep understanding for our product, so when speaking about it, we send an important message to others who seek out natural stone. Natural stone has a seemingly endless list of uses in today’s society. Over one billion tons of natural stone products — mainly aggregates and cement products in the construction industry — are used in North America on a yearly basis. Natural stone’s enduring properties in the building stone industry have been recognized throughout mankind’s history — leaving us today with a record and linkage to the past. Although the building stone industry uses less than 1% of this total yearly usage of natural stone, the application of natural stone in both masonry and landscape projects is what people see and come to love. Most people who work in the building stone industry describe our stone with a degree of passion similar to that of artists and historians. In recent years, there has been a significant influx of manufactured stone in the marketplace that is constantly trying to replicate and compete with Mother Nature’s handiwork. The fact that the faux stone industry is trying to replicate natural stone speaks highly of the properties of natural stone, however, Mother Nature has the copyright on this product! So how does one approach the task of naming a rock or mineral? This has been a process and dilemma that has been occurring for millenniums. Generally, through the process of trial and error, people have begun to realize specific properties of rocks and minerals that made them useful to their lives. This information has been recorded and passed on to others so that a common language and set of criteria is used with those interested in geology. Often I will bring a rock sample into the first class of new geology students. I ask each student to describe what they see and attempt to name this rock. Usually I will receive as many different descriptions as there are students, along with some overlapping comments. It is clear that what each individual describes is what they see, but at this point they are not sure what to do with these observations. This provides a great starting point. I then show them what properties they should be looking for in order to observe and describe the rock sample which will later be useful in naming the rock. Most text books that describe processes of rock and mineral identification list a few key properties that are similar for each mineral of rock. Often the properties of hardness, color, specific gravity, shape and size of minerals and crystals are enough to start to narrow down a mineral or rock’s name. Depending upon the amount of information required about a rock or mineral, observations and testing can often be performed in the field. If more information is required or the properties needed to be known in order to name a specimen can’t be determined in the field, then the sample can be taken to a lab where more sophisticated methods are available. ROCKS AND MINERALS So what is a rock? In general, “Rocks” are defined as a solid, cohesive aggregate of two or more minerals, rock fragments, clay minerals, and cementing or bonding materials. The natural cement that holds these mineral grains or crystal together may vary for the different major classes of rock types, and even within a specific rock type. In order to name a rock, we must know the type of minerals or rock fragments that make up the bulk of the rock, the size of the majority of fragments or crystals, and the type of cementing minerals present. It is extremely important to know and understand the properties of rocks so that they can be best utilized in suitable applications, whether it is construction, masonry or landscaping projects. Properties of rocks and minerals The minerals, rock fragments and binding cement which constitute a rocks’ make-up exhibit very specific properties that play an important role in the rock’s integrity. Knowledge of these properties is the key to describing and naming of a rock as well as having a better understanding of how the rock will perform in a variety of applications — both indoors and exterior.Explanation of some of the more important and easy-to-perform methods used to determine properties of rocks and minerals, such as hardness, specific gravity, color and grain size will be discussed. More complex testing, such as Petrographic analysis (the study of rocks and minerals in thin sections under a microscope) has the potential to reveal, with great accuracy, properties that are not obvious or evident to the unaided eye. This procedure will be discussed later along with other technical procedures used to describe and identify rocks, minerals and their properties. Hardness A rock’s hardness is mainly a function of minerals which are contained within it along with the cementing or bonding of minerals and fine rock/mineral particles which fill the spaces (matrix) between the larger mineral grains-crystal and rock fragments.When we look at the individual minerals, each has a specific hardness which can be measured in a number of different ways. The most commonly used hardness test was developed by Frederick Mohs and is called the Mohs hardness scale. The Mohs scale consists of 10 fairly common minerals (with the exception of diamonds) of known hardness. (See table 1). Mohs hardness kits may be purchased at many scientific supply stores as well as at local rock and mineral stores. The minerals which make up the Mohs hardness kit are assigned a number ranging from 1 to 10 with the softest mineral being talc and the hardest mineral being diamond. The minerals in Mohs hardness kit are: talc=1, gypsum=2, calcite=3, fluorite= 4, apatite=5, feldspar=6, quartz=7, topaz=8, corundum=9 and diamond=10.Hardness tests are based on the fact that a harder (higher number) mineral will scratch a softer (lower # mineral). This test is therefore a test of a mineral to resist physical abrasion or weathering. All naturally occurring minerals fall somewhere between these two end points. Mineral hardness “pick kits,” differ from a regular Mohs hardness kit, as they consist of 10 sharp pointed probes of known hardness that equate to the numbers on the Mohs scale. These picks are great to take in the field and can provide a better opportunity to scratch test smaller mineral or rock surfaces, a feature which is often difficult to perform with minerals in Mohs hardness kit. Other commonly accessible items to determine hardness, especially in the field, are our fingernail with a hardness (H) of 2. 5, a copper penny H=3, steel knife blade H=5.5-6, a hardened steel nail H=7, and a mason’s drill bit or emery cloth H=8.5. Knowing the hardness of a mineral is one of the most important properties to identify when trying to determine a mineral or rock’s name. Because most rocks are made up of more than one mineral it is essential when determining hardness that a particular mineral fragment or crystal be isolated and tested. Scratching the whole surface of the rock may give an average hardness of the rock especially if it is fine grained or it may only be testing the hardness of the mineral cement binding the particles or crystals together. When trying to determine the hardness of a rock it may be helpful to send a sample to a lab which can determine the breaking force measured of the rock in pounds per square inch. Color Colors can be both an asset and a distraction in trying to name a mineral or rock.Pick up any geology text book or mineral guide and the first two properties listed are generally mineral color and hardness.With very few exceptions, every mineral is one specific hardness, i.e. quartz H=7.Color of many minerals can vary greatly, and this is largely due to minute amounts of contained impurities as well as structural defects in crystal structure. Quartz is an excellent example of color variation. Pure crystalline quartz is colorless and glass/water– clear. If quartz contains trace amounts of iron it will take on a purple tone and is called amethyst. If traces of manganese or titanium are present, it is called rose quartz.If the same glassy-clear quartz was buried within the earth’s crust and exposed to natural specific processes, the mineral would change to a brown or black color and be called smoky quartz. Other colors that quartz may appear are blue, yellow (citrine), red and green. No matter which color quartz is, it will always have a hardness of 7. Other minerals with similar colors to any of the varieties of quartz colors could be separated from quartz largely on the basis of hardness. Therefore, the property of mineral hardness is a more discerning characteristic than the property of color. IDENTIFYING AND NAMING ROCKS There are more than 4,000 minerals occurring at or near the earth’s surface, which may make the task of naming a rock or mineral seem daunting or overwhelming.However, in general, the list of minerals which make-up the vast majority of rocks is small consisting primarily of four minerals: quartz, feldspars, calcite-dolomite and clay minerals. The most common cementing agents bonding these minerals together are quartz, calcite or iron oxides, and sometimes a combination of all three.With this information, the task of naming a rock becomes more manageable. Knowing the characteristic properties of the mineral’s present size of mineral crystals or fragments, the natural minerals bonding the rock and mineral fragments together have enabled geologists to create tables to assist in identifying and naming of rocks (See Table 2). Naming a rock Along with the majority minerals — quartz, feldspars, calcite-dolomite (carbonates) and clay minerals — are several minerals which may be present in very small amounts of the total rock’s volume, however, their presence can significantly alter many aspects and properties of the rock such as color and integrity. One of the more common of these minerals is pyrite (fool’s gold)- iron sulphide. Minor concentrations of pyrite in a rock can cause staining and physical and chemical break down of the surrounding rock. The natural cementing minerals often distinguish and differentiate rocks that fall into a broadly classified group of rocks. The five most common minerals present in sedimentary rocks are also present as major constituents in following articles discussing metamorphic and igneous rocks so now would be a good time to learn a few of their easily identifiable characteristics and properties. A. ) Quartz Quartz(SiO2), also referred to as silica, has two very important properties which make this mineral so very important in sedimentary rocks. These two characteristics are hardness (H=7) and its chemical inertness. Because of these two properties, sedimentary rocks containing large amounts of quartz fragments and cement are very resistant to natural and man-induced physical and chemical weathering. Quartz is the hardest of all the most abundant minerals making up sedimentary rocks. Quartz may be present as colorless, water-clear to milky white crystals, grains or fragments, as well as the many colors previously mentioned.Quartz has been given many different names depending upon its color, but color variations do not affect this mineral’s two most important properties; its hardness and solubility remain the same.These two properties alone make sedimentary rocks containing high concentrations of quartz minerals and cement very desirable especially for construction and in the building stone industry. B. ) Feldspar Feldspars (K,Na,Ca,Si3O8) are a group of minerals called silicates and are the most abundant minerals within the earth’s crustal surface rocks. Feldspars are somewhat softer than quartz — having a Mohs hardness of (H=6) — and are therefore more susceptible to natural and manmade physical weathering.Natural chemical weathering of feldspar releases some elements into solution, but of more significance, is the production of clay minerals. Clay minerals may become incorporated in sediments that eventually lithify to become sedimentary rocks. These clay minerals may affect the integrity and overall hardness / strength /durability of the sedimentary rock in a detrimental way, especially for rocks used in the building stone industry.It is therefore important to know if clay minerals are present and what type of clay mineral they are. The location and percentage of clay minerals within a rock is of upmost importance. Feldspar minerals range in color from pink to white to dark iridescent almost black colors. Feldspar content in sedimentary rocks may produce a large variation in colors, and the overall hardness of the rock could range from 3 to 6 depending upon the degree of weathering that has occurred within the feldspars. C. ) Calcite/Dolomite Calcite (CaCO3) — Dolomite (CaMg(CO3)2 are referred to as carbonate minerals and are widespread throughout the planet’s crustal rocks, most commonly appearing as limestone.Limestone starts off as accumulation of calcite crystals, shells and skeletons. This calcite may later be altered to the mineral dolomite, sometime after its precipitation or during formation into rock. There are very few pure calcite limestone deposits in the world.Most have experienced some degree of alteration transformed to dolomite over time. Dolomitization (the process of turning calcite into dolomite) occurs when Ca ions in calcite (pure limestone) are replaced/substituted by Mg ions.Magnesium ions are in solution, which passes through the limestone sometime after its formation. Generally older limestone deposits have a greater chance of turning partially or being totally transformed into dolomite. Because of the process of dolomitization, most limestone varieties range in hardness from 3 to 4 (hardness increases with a greater percentage of dolomite) and variations in color may range from snow white to gray, beige to brown, pink, purple, blue, yellow and orange.Like other minerals and rocks, the color variations are often due to trace elements or impurities within the crystal structure or as particles trapped between grains and crystals of the rock.Limestone is the softest of the common sedimentary rocks used in the building stone industry. The multitude of applications of this beautiful stone used throughout the building stone industry is a great testimony to its significance. Limestone has been extensively used throughout mankind’s history because of its widespread abundance, beauty and ease to work with for architects, quarries, contractors, masons and sculptors. D. ) Clay minerals Clay minerals are a family of minerals which largely result from the chemical breakdown of feldspars and the alteration of volcanic ash occurring in the natural weathering cycle. Clay minerals tend to be very small, soft, platy in shape and often will fill spaces between rock and mineral grains within a rock. They may also make up layers of clay, which originated as layers of volcanic ash. Some of the more common clay minerals are kaolinite, illite, chlorite and montmorillonite. Colors of clay minerals are varied occurring in shades of light white, brown to green. These clay colors can also affect the overall color of the host rock in which they occur. One very detrimental property of clay minerals is that they absorb water and can expand up to 100 times their size.Wetting and drying cycles in sedimentary rocks containing clay minerals often results in expansion and contraction of clay minerals, a process which is often more detrimental to the physical destruction of rock than damage done by freeze-thaw cycles.For this reason, the presence of clay mineral in natural building stone should be considered a red flag. Determining the presence and type of clay minerals in rock is difficult because of their small size. Electron microscope or X-ray diffraction analysis may be required to accurately identify the clay minerals which may be present in a rock. Since each type of clay mineral responds differently to weathering processes, it is important to determine which clay mineral is present and then become familiar with its properties. This information may be found from a lab testing for the clay minerals or by researching the specific clay mineral once it has been identified. Each of the three broadly identified rock groups consists of rocks that have their own “personality.” This introduction has hopefully laid a simple yet sound set of criteria to form “the bedrock” of geological methods employed in recognizing and identifying minerals and their properties. These principles and procedures may be used for rocks from each major category. This information will assist in enabling a common nomenclature that is unique to each rock group. A better understanding of the overall significance of these rock and mineral properties will be extremely important when selecting natural stone for specific projects. Sedimentary rocks Characteristics of sedimentary rocks Sedimentary rock results from the accumulation of detrital (clastic) sediments produced by the weathering of pre-existing rocks or minerals, followed by their transportation, deposition and lithification resulting in a sedimentary feature known as bedding (layering). Gravity aids in the accumulation of inorganic chemical precipitates, the products of biochemical processes (shells and skeletons) and build-up of organic material (plants – coal) which can result in layering (bedding) of great thicknesses of rock covering vast areas. Sedimentary rocks on average tend to be the softest of the three basic rock groups, averaging a hardness of 3 – 4 on Mohs scale. Exceptions to this average low hardness do occur along with other desirable properties, resulting in many clastic sedimentary rocks having a multitude of applications within the architectural and building stone industries.The most outstanding characteristic of sedimentary rocks are: 1. Layering (bedding) of various thicknesses with flat upper and lower tops and bases (bedding plane surfaces). Clastic sedimentary rock layers (beds) tend to be thinner and lesser in aerial extent than nonclastic (chemical) rocks such as limestones. 2. Transportation of sediments mainly occurs by water and less commonly by air and ice. 3. Most sediments are deposited in water, mainly oceans. 4. Sedimentary rocks often contain fossils and fossil imprints along with trace fossil tracks thereby recording some of the earth’s prehistoric past life. 5. Sedimentary structures such as wave ripple marks and stream channel beds are frequently found in sedimentary rocks, which indicate past environments of the earth’s history. Geologists have divided sedimentary rocks into two categories: Clastic Sedimentary Rocks and Non-Clastic Chemical Sedimentary Rocks. CLASTIC ROCKS Sedimentary rocks make up between 80 to 90% of the rock exposed at the Earth’s surface, but they are only a minor constituent (about 8%) of the volume of the entire Earth’s crust. Sedimentary rocks form at or near the Earth’s surface by the accumulation of rock or mineral fragments (clastic rocks) or the precipitation of dissolved minerals (nonclastic rocks). Clastic sedimentary rocks result from the erosion of a parent rock by physical and chemical weathering processes. This is followed by transportation by water, wind, ice or gravity. In most instances, the transported particles are re-deposited as sediments in layers, referred to as beds, of various thicknesses, generally having flat upper and lower surfaces called bedding planes.These layers of sediment overlay each other (build up) over time, and if geological conditions are favorable, the sediments become compressed and naturally cemented (lithified) — becoming rock. Most clastic sediments are deposited in an environment of fresh or salt water (lakes, oceans and seas). Environments where clastic sediments are deposited in water result in more widespread distribution and greater consistency in rock bed thickness.Other sediments transported by wind, ice or gravity may be re-deposited, buried, compressed and cemented together — becoming rock. Environments such as this may result in rock layers having less uniformity with respect to bed thickness, range in particle sizes and smoothness of bedding plane surfaces. Over time, the burial process results in compression of the sediments consisting of rock and mineral fragments. Spaces between the mineral or rock fragment (matrix) are partially or totally filled with finer fragments along with naturally occurring minerals which were in solution and crystalize to act as cement. When this happens, the sediments are lithified (cemented together) and a sedimentary rock has formed. Size of the clastic particles within the rock is the main feature used to name each Clastic rock. This is illustrated in the table found on page 88. There are four main types of clastic sedimentary rocks. These are shale/ mudstone, siltstone, sandstone and conglomerate/ breccia. In general, most Clastic rocks have a gritty feel or appearance. 1. ) Shale / Mudstone Shale and mudstone are primarily made up of very small size fragments of rocks and minerals, generally ¹/256 mm in diameter or less, and are referred to as “clay sized” particles, which differ from “clay minerals.” Shale will split into layers, while mudstone tends to be more massive.These rocks also often contain “clay minerals” which are a group of minerals that have unique properties that may greatly affect the rocks integrity. Due to the very fine particle sizes that make up shale and mudstone, these rocks feel very smooth to touch and with the unaided eye, individual grains cannot be seen.Shale and mudstone are primarily used in the manufacturing of bricks, ceramic products, aggregates in landscaping and as potential source rocks for oil, gas and coal resources. 2. ) Siltstone Siltstones are sedimentary rocks that are made up primarily of particle sizes that fall in the silt size range which is ¹/256 mm to ¹/16 mm in diameter. Siltstone layers (beds) vary in natural thickness — from 1 mm to a few meters — and have smooth flat bedding plane surfaces, which aids in the quarrying process. These smooth bedding plane surfaces are planes of weakness, allowing the rock to be physically split producing smooth flat surfaced rocks such as natural thin veneer, flagstone, wall stone, etc. Because of the natural smooth bedding planes, siltstone requires less mechanical processing in both the quarrying and final preparation for use. Siltstone has a slightly gritty feeling to touch or to rub your finger nails over, and the unaided eye can distinguish many of the small mineral and rock fragments that are cemented together.The spaces between the silt-sized grains are often filled with finer rock and mineral particles called matrix, along with one or more natural cements. Siltstone has many uses in the construction industry as aggregates and a source of silica, and in the building stone industry as naturally occurring thin veneer, flagstone, ledgestone and decorative landscape boulders. 3. ) Sandstone Sandstones are sedimentary rocks that are mainly composed of particle sizes which fall within the sand size range which is ¹/16 mm to 2 mm in diameter. Sandstone layers can be quarried and split along their natural bedding plane to produce excellent stones for use in masonry and landscaping projects. Sandstone pieces feel gritty to touch, much like the various grades of sandpaper as the range in particle sizes are similar to the range of sand paper grit — i.e., coarse to fine grit. When observing sandstone pieces, it is easy to see individual grains with the unaided eye. Spaces between the sandsized grains (the matrix) are filled with finer-sized rock (silt and clay sizes) and mineral particles, as well as one or more of the natural cementing minerals which bind all mineral particles to form the rock.Sandstone is primarily used in the building stone industry because of its relative ease to quarry and work with. Often sandstone layers have flat surfaces, which reduces the cutting that is required in other types of natural stone. Many sandstone layers are also very uniform in thickness, making it easier to work with when being quarried and during the shaping and sizing of natural stone products either in dimensional stone fabrication shops or by stone masons in the field. Landscaping boulders and freestones used in carving blocks for sculptures and other building products are another important use of sandstone in the building stone industry. Of all sedimentary rocks, sandstones have the most variations in hardness ranging from 3 to 7 on the Mohs hardness scale. This variation in sandstones hardness is of utmost importance to all persons involved in building with natural stone. Reasons for these variations will be discussed in detail later on. 4. ) Conglomerate/Breccia Conglomerate and breccia are sedimentary rocks where the majority of mineral and rock fragments are greater than 2 mm in diameter.If the grains are rounded, the rock is called a conglomerate. If the fragments are angular in shape, the rock is called a breccia. These sedimentary rocks generally are not able to be quarried with flat smooth surfaces, but rather as large blocky rock pieces, which can be saw cut into flat slabs of various thicknesses, used as ornamental or landscape boulders, or crushed for aggregate in the construction industry. A simple summary of Clastic Sedimentary rocks based on particle sizes is as follows:clay-sized particles result in shale or mudstone; silt-sized particles form rock called siltstone; sand-sized particles produce sandstone; gravel-sized particles will form rock called conglomerate or breccias. This simple classification table used by most geologists (page 89) also considers the type of mineral or rock fragment which comprises the majority of the rock. In general, the further the mineral or rock fragment that has weathered off the parent rock has traveled, the better sorted, more rounded and smaller the fragments will be. This process is referred to as the maturity of the sediments.Mature Clastic sediments tend to be largely composed of the mineral quartz and are often the hardest Clastic Sedimentary rocks.Generally, mature sedimentary rocks are quartz sandstones and siltstones. Maturity of Clastic sediments is an important property which makes these rocks so favorable to be used in the building stone and construction industries as aggregates and sources of silica for making of specialized erosion resistant cements and glass products. NON-CLASTIC/CHEMICAL SEDIMENTARY ROCKS Chemical Sedimentary rocks, often referred to as carbonates, of which limestone forms the largest component, are mainly composed of the mineral calcite (calcium carbonate) and form primarily in shallow warm marine conditions. Over time, the growth and precipitation of calcite crystals accumulate on an ocean floor as they rain down out of solution under the influence of gravity. Most Chemical Sedimentary rocks have a crystalline appearance. When conditions are favorable for precipitation of calcite crystals to accumulate over long periods of time, and over large geographic areas, the layers of limestone can be several hundreds of feet thick and cover thousands of square miles. This process can be observed happening today in many of the tropical oceans around the globe. Carbonate rock layers tend to be much thicker and more widespread than most Clastic Sedimentary rocks and their bedding plane surfaces are generally not as smooth as those of most Clastic Sedimentary rocks. Some Chemical Sediments have a large biological contribution to their origin.For example, many shells or skeletons are made of calcium carbonate (calcite) or silica dioxide (quartz). Areas where these organisms flourished and died may have thick and widespread accumulations of skeletal parts or shells piled up on the ocean floor together with the calcite crystals precipitating out of water. These accumulations are then buried and lithified (cemented together) to become “coquina” limestone. These processes have resulted in enormous and extensive limestone deposits covering large areas of North America and most other continents.The largest use of limestone is in the manufacturing of cement and aggregates in construction. Limestone also plays a major role in the natural building stone industry being used primarily for structural purposes, cladding and fine sculptured finished products in both exterior and interior applications.Limestone popularity is due to many factors such as its beautiful array of colors, surface textures and patterns combined with widespread distribution and ease of quarrying and shaping into desired natural stone products. The most important property of limestone is its relative softness with respect to other natural stone used in the building industry. Being one of the softer building stones to work with, it is therefore less costly to manufacture into dimensional stone sizes and custom carved stone pieces required in a multitude of special natural building stone projects. Limestone is also an important resource in landscape projects, such as armouring riverbanks for flood mitigation, aiding in reducing the acidity (pH) of waters and accentuating natural landscapes with accent feature boulders. EVAPORITES/SALTS Another type of chemical sedimentary rock is formed when a body of water (ocean or sea) becomes isolated from the main ocean and begins to evaporate. As evaporation takes place, the concentration of dissolved minerals in solution increases until they begin to precipitate out onto the floor of this evaporating body of water. Such conditions result in the formation of layers of salts such as anhydrite and gypsum (CaSO4-CaSO4H2O), halite (NaCl, common table salt), sylvite (KCl, potash fertilizer) and many other rarer salt minerals.Vast areas of North America are underlain by extensive salt beds which resulted from the evaporation of ancient isolated bodies of water. These salt deposits have enormous use in many aspects of our everyday lives. Gypsum is used in the construction industry mainly for wallboard and as an ingredient for cement, but has no largescale use in the building stone industry. ORGANIC SEDIMENTS Organic Sediments also are significant sedimentary rocks as accumulations of plant and animal bodies over very large periods of time have left us with massive coal and petroleum resources contained within the surrounding sedimentary rocks.These organic sediments have little or no use in the building stone industry. Applications of sedimentary rock SANDSTONE AND SILTSTONE With respect to the Clastic Sedimentary rocks, sandstone and siltstone are most often used in the building stone industry. The more mature the sediments are (higher amounts of the mineral quartz as the major grains and matrix), the harder and more resistant to physical and chemical weathering they will be. When combining these mature sediments with a cementing agent of the mineral quartz, we have a rock that is called quartz-sandstone or quartz-siltstone with an overall average hardness between 6 and 7. These mature Clastic rocks are as hard as most granitic rocks, which will be discussed in our next article. If the cement in these rocks is other than quartz — i.e., calcite or an iron oxide — the overall hardness and durability of the rock will be less than the previous example. This is due to the fact that the calcite and iron cements have a hardness range of 3 to 4 and are more soluble than quartz cement. Clastic rocks containing less mature sediments have less well sorted minerals and rock fragments with respect to shapes and sizes. These “immature” Clastic rocks are therefore less resistant to physical and chemical weathering than rocks composed of mature sediments. This is especially true if there are clay minerals present in these rocks, and if these rocks are exposed to weathering conditions where many cycles of wetting and drying are experienced. SHALE/MUDSTONE Shale or mudstones are rarely used in the building stone industry because of their softness and inability to withstand physical and chemical weather. These rocks are of great significance to the construction and industrial sectors and in landscaping as aggregates.Shale and mudstone are also important as a source for some rare elements that become trapped within the clay minerals and these rocks may be a source for specific clay minerals used in ceramics. CONGLOMERATE AND BRECCIA Conglomerate and breccias are sometimes used in the building stone industry but they often are more difficult and expensive to quarry and process due to their more massive and irregular beds. If the minerals and rock fragments making up these rocks are mature, then this class of Clastic rocks can be extremely hard — similar to mature sandstone and siltstone. Often conglomerate boulders are saw cut after being quarried, which results in wonderful patterns of colorful pebbles seemingly frozen in a matrix of finer grained minerals and cement.Conglomerates and breccias are often called pudding stone because of this appearance.Once again, a huge feature in this rock’s durability comes down to the presence of clay minerals and the cementing mineral. Quartz will be hard and inert resulting in the rock being very durable, while calcite or iron oxide cement will be softer and more soluble resulting in a softer rock.Clastic rocks can make excellent building stones, especially if composed largely of mature sediments. The biggest deterrent to using clastic rocks in building stone and landscaping are the presence of clay minerals and softer soluble cements holding the rock together. LIMESTONE/DOLOMITE Limestone has a long and distinguished history of use throughout the broad spectrum of projects within the building stone landscape industry. Natural variations occurring in sedimentary rocks As with all rocks there rarely is a quarry site where the consistency of the rock remains the same throughout the whole area. Inconsistencies are more frequent in units of clastic rocks than the chemical sedimentary rocks. For all sedimentary rocks, lab tests provide the most reliable information. A petrographic analysis will provide accurate descriptions of minerals, rock fragments, fine particles, grain orientation, porosity and permeability and a list of other rock properties that cannot be identified in a hand specimen. This petrographic information is extremely important to understanding the nature and properties of rock, and for achieving the level of detail necessary in naming rocks. Sedimentary rock summary Sedimentary rocks have a greater use in construction and manufacturing than their use in the building stone industry i.e. aggregates and cement products. Where they are used as natural building stone, their inherent properties make these rocks attractive.Sedimentary rocks are extremely important due to their availability, low costs of quarrying, variations of colors within a stone and between similar stones, and ease of shaping into usable products – i.e., external sandstone patterns and textures and the fact that many are used to display their natural stone surfaces Hopefully the discussion, examples, photos and tables provide valuable insight into identifying and understanding sedimentary rocks. The articles that follow will be presented in a similar format so that processes of identification will become more routine.The next article in the fall 2015 issue will discuss Granitic rocks which have played significant roles in the building stone industry for thousands of years and continue to be coveted as a wonderful natural stone with many applications. Louis Kamenka received his Undergraduate Geology degree from the University of Alberta, Edmonton, Alberta, Canada in 1976, and later researched and studied in the area of environmental geology “Reclamation of Open Pit Mines in the Rocky Mountains,” receiving his Masters degree in Geology from the University of Alberta in 1982. Louis spent many years employed as a research scientist /geologist with the Geologic Survey of Canada-Western Canadian Region and has worked as a consulting Geologist for many different companies across Canada. Since 2000, Louis has owned and operated a building stone boutique quarry which specializes in interesting rocks that record fascinating pages of the Earth’s History. Louis continues to be engaged in geological consulting projects, instructing geology courses to tour companies and nature guides, as well as quarry and geology tours for many special events and interest groups such as International Geologic conventions and environmental awareness programs. Stone Testing Resources Material Testing, Boise, ID www.mti-id.com Testing Engineers International, Salt Lake City, UT www.tei-test.com/ Wiss, Janney, Elstner www.wje.com/ Aecom www.aecom.com Ceramic Tile & Stone Consultants, www.ctasc.com Natural Resources Canada, www.nrcan.gc.ca
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