Indiana Geological Survey Introduction to Minerals of Indiana€¦ · Minerals are the building...
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Indiana Geological Survey Introduction to Minerals of Indiana€¦ · Minerals are the building blocks of rocks. Some minerals are mined for their useful properties or compounds and
Industrial minerals form the foundations – literally and figuratively – for modern society. Note that the term “industrial minerals” encompasses rocks as well as minerals in common usage. Indiana limestone makes the striking main library building at Indiana University in Bloomington.
Per capita use of minerals amounts to several thousand pounds.
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Use of well-known metals such as zinc, copper, lead, and others is minor compared with the tonnages of industrial minerals such as stone, sand and gravel, clays, cement, and other non-metals.
Much of your house is mined from the Earth.After “Out of the Rock” by the National Energy Foundation
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If a commodity cannot be grown, it must be mined.
INDUSTRIAL MINERALS AROUND THE HOUSE
Carpet
Glass/Ceramics
Vinyl Flooring
Glossy Paper
Cake/Bread
Plant Fertilizers
Toothpaste
Lipstick
Baby Powder
Calcium carbonate
Silica sand, limestone, talc, lithium, borates, soda ash, feldspar
Calcium carbonate, clay, wollastonite
Kaolin clay, limestone, sodium sulfate, lime, soda ash, titanium dioxide
Gypsum, phosphates
Potash, phosphates, nitrogen, sulfur
Calcium carbonate, sodium carbonate, fluorine
Calcium carbonate, talc
Talc
ITEM MINERALS NEEDED TO PRODUCE THEM
Minerals are used around the house in many common products.
More industrial minerals around the house, page 2.
Minerals are also used at your school.
After “Out of the Rock” by the National Energy Foundation
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Minerals are often used for items not normally considered a product of mining. Minerals are often treated or combined with other materials to create building materials.
Specimen courtesy of D. Cook, Indiana University Department of Anthropology
Minerals are in your teeth, bones, and even kidney stones.
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Minerals are in your teeth, bones, and even kidney stones.
All minerals are made of naturally occurring elements.
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Periodic Table of the Elements.
crystal
This diagram shows the relationships between atoms: atoms form molecules which come together in minerals as a collection of unit cells. Unit cells form minerals and visible crystal forms.
collection ofunit cells
unit cell
moleculeatoms
ELEMENTS AND MINERALS
After Mineralogy, 1998, Dexter Perkins
mineral
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Atoms combine in specific proportions to make molecules based on well-known chemical principles. These molecules can come together in three-dimensional arrays to form minerals. If sufficient time and space is available, beautiful geometric solids called crystals can grow.
GraphiteDiamond
The arrangement of atoms is important. The element carbon (C) can form diamond -- a hard, clear mineral -- or graphite -- a soft, gray mineral --depending on the crystal structure.
STRUCTURE
Hard, bright, gem
Soft, gray, lubricant
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Unique arrangements of unit cells can only occur in limited ways. Mineralogists study the pattern of unit cells to determine mineral structures. The arrangement also controls properties of the mineral.
A naturally occurring, generally inorganic solid that has an ordered arrangement of atoms and specific chemical and physical properties.
DEFINITION of MINERALS and ROCKS
1. Naturally occurring: Not man-made (but there are synthetic “gems”)
2. Solid: Hard; not liquid or gas
3. Ordered arrangement of atoms: Made of atoms that are arranged in three dimensions; crystalline
Is made of one or more minerals, usually occurring in large masses.
Mineral:
Rock:
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Minerals are the building blocks of rocks. Some minerals are mined for their useful properties or compounds and are known as industrial minerals. Industrial rocks are combinations of minerals that make large, discrete bodies of the earth. Rocks are composed of billions and billions of separate mineral particles. Limestone is made from calcium carbonate – the mineral, calcite.
ROCKCYCLE
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There are three main categories of rocks. Igneous rocks form from melted earth materials and have interlocking crystals. Sedimentary rocks form from weathered and transported particles of pre-existing rock, or by chemical precipitation from waters. Metamorphic rocks form from rocks or sediments that have been subjected to heat and pressure. One kind of rock can be transformed into any of the others by geologic processes.
TYPICAL ROCK TEXTURES
IGNEOUS SEDIMENTARY METAMORPHIC
Crystalline(interlocking)
Fragmental(clastic)
Foliated(banded)
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Typical rock textures.
IDENTIFYING MINERALSProperties used by geologists
Shape: Symmetry, form, habit, twinningCleavage: Tendency to break along the rows of atoms; shiny, flat
Density: Weight (relative to equal volume of water)Appearance: Transparency, color, luster, fracture Streak: Color of the fine powder from a mineralSpecial Properties:
4. Chemical reactions5. Action in heat/flame6. Taste
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Geologists use simple techniques to identify minerals and rocks. More sophisticated techniques are also used for special studies.
One way to help identifyrocks is to use a “scratchhardness test.” The items listed on the right side will make a visible scratch on anyof the minerals listed abovethem.
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Moh’s Hardness Scale is used to identify the hardness of minerals.
The most common Indiana mineral is calcite or calcium carbonate (CaCO3).
* Several varieties
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More than 100 different kinds of minerals have been reported from Indiana. Many others probably occur in very small amounts. Here are the most common minerals found.
Crystal structure of calcite. When allowed to freely grow into open spaces minerals can form beautiful geometric solids called crystals.
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This is a model of unit cells in calcite. Red is oxygen; black is carbon; white represents calcium. Layers of CO3 alternate with layers of calcium. The unit cell is outlined with twine and shows the rhombohedral structure.
CALCITE
Calcite is calcium carbonate. It fizzes in acid. It is usually white orcolorless, but can be other colors because of impurities in it. It may havemany outward shapes, but always breaks into little pieces shaped like rhombo-hedrons. Calcite makes up the rock called LIMESTONE. Limestone is used asfertilizer, aggregate, building stones, and to make cement.
rhombohedralcleavagefragment
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Calcite.
Crystals of calcite with trigonal pyramids.
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One crystal form of calcite has three-sided (trigonal) pyramids that terminate the crystal.
A vug (open space in rock) with iridescent calcite crystals in a limestone rock.
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Crystals require open space to form completely. The vug contains one-half inch crystals. The surrounding rock is made of very tiny crystals.
Calcite crystals can also be found in geodes.
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Open space often occurs in geodes. Geodes sometimes contain excellent, large crystals.
A related mineral with the same chemistry as calcite but a different crystal structure is aragonite which forms white, needle-like crystals.
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The mineral aragonite has the same chemistry as calcite, but forms in very different crystals. This aragonite sample occurs within a weathered geode from Monroe County, Indiana.
Indiana limestone dissolves in acidic groundwater. These solution features are often seen in dimension limestone quarries.
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Water traveling through soil picks up small amounts of carbon that cause the water to be slightly acidic. Limestone dissolves in acidic waters. Dissolution leads to open spaces like these grikes and eventually to cave formation.
Indiana has many cave formations in limestone rock, called speleothems. Speleothems are made of calcite or aragonite.
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Water charged with dissolved calcite and other minerals flows through the rock. If water evaporates, such as in a cave, the dissolved mineral can crystallize on the cave walls, floors, and ceilings to form fantastic shapes called speleothems.
Curved faces
DOLOMITE
Dolomite is calcite with magnesium added. It fizzes in warm acid. It is usually pink or white and has curved faces. It is a common mineral and is used for building stones and for making heat-resistant bricks for furnace linings.
Pearlyluster
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Magnesium atoms replace every other layer of calcium in the dolomite structure. The magnesium restricts certain uses of limestones that contain significant amounts of dolomite.
Example of dolomite in pink crystals with purple fluorite crystals.
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Dolomite crystals.
Cubic crystals Octahedralcleavage
Often zoned
FLUORITE
Fluorite is calcium fluoride (CaF2). It will change color under fluorescent light; this property is called fluorescence. It is usually purple, light green, yellow, or clear. It forms in cubes, but cleaves into octohedrons. It is used for a flux in smelting iron, for decorative stones, in the chemical industry, and for making optical equipment.
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Fluorite.
Yellow fluorite with white calcite
Fluorite
Calcite
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Enlarged (approximately 5X) image of calcite and fluorite crystals. Fluorite forms cubic crystals and calcite, in this case, is in the form of a hexagonal (six-sided) crystal with flat terminations.
This is a sample of a rare, fibrous form of fluorite.
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Fibrous fluorite is almost unknown except for one area in Great Britain and Harrison County, Indiana. Fluorite generally forms as cubes.
White gypsum and purple fluorite
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Pseudomorph is a mineralogic term that is used for a mineral which forms in the shape of a different mineral, rather than its preferred or normal shape by replacing a pre-existing mineral. Here, fluorite (purple) has replaced, pseudomorphically, gypsum crystals.
The mineral siderite (FeCO3) forms concretions. This one also contains white clay minerals.
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Concretions are round to oval segregations of hard mineral matter that occur in sedimentary rocks. Concretions sometimes contain secondary (late-formed) minerals.
Magnified image of quartz geode containing a barite (BaSO4) crystal.
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Barite does not occur in mineable amounts in Indiana, but is used in well-drilling mud, paint, and many other uses. A beautiful crystal of barite was found in a geode near Lake Monroe in southern Indiana.
Delicate blue celestite (SrSO4) crystals
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Celestite contains strontium and is used to make bright red fireworks.
Crystals display special features inside. Here, a pointy, white phantom crystal is inside the clear calcite.
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Crystals can grow in different episodes if a pre-formed crystal can be seen through the later generation of mineral, the inner crystal is called a “phantom”.
Petroleum is included in this calcite crystal giving it a brown color.
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As crystals grow, they can include or grow around other materials such as water, petroleum, or minor minerals. These are known as “inclusions”.
This calcite sample has inclusions of a dark sulfide mineral, marcasite.
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Inclusions can affect mineral properties and appearance. Sometimes, inclusions can give valuable data about conditions of mineral formation or birth. Minerals can even include organisms.
Chert, a very fine-grained variety of quartz (SiO2), was used extensively by Native Americans.
chert spearpoint
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Quartz is the most common mineral on Earth. It can be found in many different guises. Chert is made of very fine, usually elongate crystallites of quartz. Impurities cause chert to appear in many colors. Native Americans used chert extensively for weapons, tools, and even ceremonial objects.
Crystals of quartz are common in geodes. This is a geode cut in two.
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Pure quartz is generally clear or white. These large (one inch) crystals grew in a mosaic pattern inside the open space of a geode.
The outside of geodes are bumpy and have spherical forms.
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The ugly outside of geodes belie the beauty that can exist within.
This is a typical geode in the limestone bedrock.
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A geode in the wild, as it is found in rocks of south-central Indiana.
Brassy yellow
PYRITE
Pyrite (FeS2) is iron sulfide. It is also called “fool’s gold” because it is a metallic golden color. Harder than gold, sparks will fly if it is hit with a hammer. It forms in cubes, and is not valuable by itself. Fossils are often replaced by pyrite. Pyrite is the most common sulfide mineral in Indiana.
Darktarnish
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Pyrite.
This pyrite nodule occursin a black oil shale.
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Pyrite is a common secondary mineral in Indiana’s oil shale and coal beds. Pyrite contains sulfur, which when burned, can become a gas that enters the atmosphere. Limestone is used to remove sulfur compounds from coal-fired power plants.
Good crystals of pyrite are common.
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Good crystals of pyrite can be beautiful and are sought after by mineral collectors commonly known as “rock hounds”.
More typical occurrences of pyrite are in crystalline groups like these. This sample shows pyrite in limestone.
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Pyrite more typically appears as small metallic, brass-colored crystals or masses.
Marcasite is also iron sulfide, but forms in a different crystal form as apseudomorph of pyrite.
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Marcasite is a polymorph of pyrite. A polymorph is a mineral with the same composition as another mineral, but which forms in a different crystal shape or form. Aragonite and calcite are also polymorphs.
The brown mineral sphalerite (ZnS) forms very large crystals in some cases. This crystal is about one foot long.
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Sphalerite is unusual in Indiana. This large specimen was found in a reef near Delphi, Indiana. Sphalerite provides the metal zinc, which is used in cars, steel making, and many other industries.
Sphalerite also occurs in bands. Here, sphalerite and pyrite form the bands.
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Minerals sometimes form in artistic arrays.
The shiny, cubic mineral galena (PbS) is rare in Indiana.
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Galena is very rare in Indiana, but was mined extensively in southern Illinois. Galena is the mineral source for lead which is used in car batteries. .
The rare mineral millerite (NiS) is the spidery, dark crystal growing upon quartz in this geode.
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Millerite is exceedingly rare throughout the world. It forms accicular (needle shaped) crystals. This specimen came from southern Indiana.
Iron oxide such as this was used for red pigment by Native Americans.
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Iron reacts with oxygen in the air to form many colorful minerals. This iron oxide concretion was found at a gravel pit.
Small crystals of resistant, so-called “heavy minerals,” including gold (Au), can be concentrated from stream sediments. These minerals were brought to Indiana by glaciers.
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As rocks weather, most minerals are destroyed or transformed. A limited suite of so-called “heavy minerals” retain their properties under severe conditions of weathering and transport. They can be carried far from their origin. Sand deposits in Indiana contain heavy minerals that originated in Canada. Some even were mined in the Morgan and Brown County areas.
The calcite crystal pictured here is from Indiana. The journal Rocks and Minerals featured Indiana minerals in this 1986 issue.
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Collectors prize well-formed crystals. Rock and mineral shows bring together collectors who exhibit their prize specimens. Several books and magazines feature minerals and mineral collecting.
Contact:Indiana Geological SurveyAn institute of Indiana University
