QUARTZ is the most common of all minerals, making up about 12 percent of the earth’s crust. There are two main types of quartz—crystalline quartz and dense, crypto-crystalline (submicroscopic) quartz. Many dense varieties occur in Illinois, probably the most common are chert or flint.
Crystals of quartz are typically six-sided, elongated, have sharply pointed pyramid-like ends, and are apt to grow together forming twins. Good crystals are rare in Illinois, and the crystal structure is not apparent in the commonly occurring grains and masses.
Quartz is brittle and hard. It may be colorless or tinted, transparent or translucent, but more commonly it is white and nearly opaque. Transparent quartz looks much like ordinary glass, but it scratches glass easily. It has a glassy to brilliant luster and breaks irregularly or with a good conchoidal fracture.
Some varieties of quartz that are used for semiprecious gems are chalcedony, agate, onyx, and jasper. Chalcedony is waxy, smooth, generally translucent, white to gray, blue, brown, or black. Agate is a form of chalcedony that has a mottled or variegated banded appearance and may be yellow, green, red, brown, blue, gray, or black. Onyx is agate with parallel bands that as a rule are brown and white or black and white. Jasper, an impure opaque quartz, generally is red.
Quartz occurs as rock crystal (colorless, transparent), milky quartz (white, nearly opaque), and smoky quartz (smoky yellow to gray or brown) in geodes from the Warsaw and Keokuk Limestones of the Nauvoo-Hamilton-Warsaw area and as vein and cavity fillings associated locally with fluorite, sphalerite, and galena in extreme southern Illinois. It also occurs as vug (cavity) fillings in limestones and sandstones.
FELDSPAR is the name applied to a group of minerals that are the second most common of all the earth’s minerals. All feldspars are composed of aluminum, silicon, and oxygen, combined with varying amounts of one or more metals, particularly potassium, sodium, calcium, and lithium.
The minerals are hard, have a smooth glassy or pearly luster, and cleave along two planes nearly at right angles to each other. Feldspars are fairly light weight. The streak is white, but the color of the mineral is highly variable, although potassium and sodium-bearing feldspar are commonly white or pink and most plagioclase feldspar is gray.
Feldspars are essential parts of the crystalline igneous rocks. Their decomposition products are present in most soils. In Illinois relatively small feldspar crystals can be found associated with quartz and other minerals in granite and gneiss boulders and pebbles in glacial drift.
MICA is the name of a family of complex aluminum silicate minerals that can be split easily into paper-thin, flexible sheets. If broken across the grain at right angles to the flat, smooth surface they fracture raggedly. In a single mica crystal the sheets range from more or less transparent to translucent and are arranged one on top of another like a deck of cards.
Micas are tough and somewhat elastic, soft enough to be split and scratched by a fingernail, and are light weight. They have a nonmetallic, glassy or pearly luster, although yellow mica may appear to be metallic. Color and streak depend upon the chemical composition of the mineral. Muscovite, or white mica, contains potassium and makes a colorless or white streak. Biotite, or black mica, contains iron and magnesium and is commonly dark green or black, although it may be shades of yellow or brown; its streak is uncolored.
Mica is abundant as tiny, shimmering flakes in Illinois sands, sandstones, and shales (which are then said to be micaceous). It also is common in many varieties of igneous and metamorphic rocks. White or yellow flakes may show a brilliant luster and may be mistaken for silver, platinum, or gold, but those minerals are heavy and malleable whereas mica is not.
CALCITE, a common rock-forming mineral, consists of calcium carbonate. The mineral is white or colorless, but impurities may tint it shades of yellow or gray. Transparent calcite is more rare than the tinted varieties.
Transparent calcite possesses the property of double refraction; an image appears double when viewed through a calcite cleavage block.
Calcite has a glassy luster, its streak is white or colorless. The mineral is of medium hardness and can be scratched by a penny or a piece of window glass but not by the fingernail. It is fairly light weight and effervesces freely in cold dilute hydrochloric acid.
Calcite has a variety of crystal forms but in Illinois flattened block-shaped crystals and elongate crystals with tapering points (“dogtooth spar”) are the most common. When broken, calcite cleaves into six-sided blocks called rhombs.
Crystals of calcite are found in Illinois as linings in geodes in certain limestones and shales, especially in the Nauvoo-Hamilton-Warsaw area, and as crystalline masses in limestone and dolomite. Small amounts of clear crystalline calcite are associated with various ores in northwestern and extreme southern Illinois.
Calcite is the principal mineral in limestones and occurs as a component of many concretions.
FLUORITE, or fluorspar, is made up of the elements calcium and fluorine. The mineral is easily identified by its perfect cleavage, color, and hardness.
It occurs in cubic crystals that may be twinned but is more often found as irregular masses. It can be split into diamond-shaped, eight-sided forms (octahedrons). Fluorite is commonly gray, white, or colorless, but it may be green, blue, purple, pink, or yellow. The streak is colorless and the luster glassy. It can be scratched by a knife or a piece of window glass, is fairly light weight, and is transparent to translucent.
Extensive deposits of fluorite, one of Illinois’ important commercial minerals, occur in Hardin and Pope Counties in extreme southern Illinois, where it is associated with galena, sphalerite, calcite, barite, and other less abundant minerals.
Fluorite is used to make hydrofluoric acid, to form a fluid slag in the production of iron and steel, in the manufacture of aluminum, to make many chemical products, and in the ceramic industry, in which it is used to make colored glass, enamels, and glazes.
GYPSUM, hydrous calcium sulfate, is a colorless, transparent to translucent mineral when pure, but it often is stained yellow by impurities. It has a white streak, is soft enough to be scratched by a fingernail, and is light weight.
Gypsum occurs in several forms. Selenite is a coarsely crystalline, transparent variety, composed of flat, nearly diamond-shaped crystals that can be split easily into thin sheets, have a glassy luster, and often grow together to form “fishtail twins.” Crystals of selenite occur in shales of the “Coal Measures” of southern, north-central, and western Illinois, and can be picked up at the surface.
Satin spar has crystals like silky threads closely packed together, splits parallel to the fibers, and is found as fillings in rock cracks and as thin layers in shales. Massive gypsum is granular.
Gypsum deposits occur deep underground in Illinois but thus far have not been mined.
CHERT, one of the main forms of silicon dioxide, is cryptocrystalline (submicroscopic) quartz. Most of the chert in Illinois is white or gray, but impurities stain many deposits yellow, brown, or even pink. Chert is so hard that it can scratch glass and ordinary steel. It is fairly light weight, dense, opaque, and brittle; the luster is dull.
Flint, a variety of chert, is generally dark colored, more dense, may have a glassy luster and be transparent in thin flakes. Both chert and flint have a smooth, curved (conchoidal) fracture, but flint tends to break with thinner, sharper edges. Indians used flint and chert to make arrow points and spearheads.
Chert occurs as rounded masses (nodules and concretions) or as irregular layers in limestones and dolomites in northern, western, southwestern, and southern Illinois. Because chert is hard and more resistant to weathering than limestone or dolomite, it often remains after the rest of the rock has weathered away.
Chert also is abundant in many glacial deposits because it is hard and resists solution. Streams that flow through cherty bedrock or glacial deposits carry pebbles along and concentrate them as gravel in stream channels. Cherty stream gravels are especially abundant in western and southern Illinois.
Brown chert gravels in the southern part of the state are used for road gravel. Other deposits in extreme southern Illinois, consisting of angular fragments of chert and a small amount of clay (known locally as novaculite gravel) also are used for road surfacing.
White and gray chert occur as massive bedrock deposits several hundred feet thick in Union and Alexander Counties.
PYRITE and MARCASITE are iron disulfide compounds. They look much alike but have different crystal forms. Both are brittle, hard, brassy yellow with metallic luster, and opaque. The best distinguishing feature is crystal shape. The pyrite crystals are cubes, but the marcasite crystals are blade- or needle-shaped.
Pyrite and marcasite have been mistaken for gold because they are yellow and metallic and hence are sometimes referred to as “fool’s gold”. They, however, are harder than gold, tarnish, and leave a dark streak, whereas gold is soft, very heavy, does not tarnish, and leaves a yellow streak. Gold is malleable, but pyrite or marcasite are reduced to powder if they are pounded and give off a noticeable odor of sulfur dioxide gas if they are heated.
Pyrite and marcasite are found in many deposits in Illinois. They occur as grains or larger masses in some clays, shales, and limestones. They also occur with the lead and zinc ores of northwestern Illinois and, in small amounts, with the fluorite and associated minerals in the extreme southern part of the state.
Both pyrite and marcasite are common as surface coatings, veins, and concretionary structures in coal and in dark shales associated with coal. They are referred to as “coal brasses” or “sulfur” when found as impurities in coal.
A potential use for pyrite and marcasite is in the manufacture of sulfuric acid for industrial use. Coal brasses recovered from Illinois coal have been so used.
LIMONITE is an iron oxide containing water and has a complex chemical composition. The limonite found in Illinois may be yellow, orange, red, brown, or black, but its streak is always yellowish brown. The mineral may have a glassy or an earthy luster. It may be too hard to be scratched by a knife. It is of medium weight.
Limonite is common and occurs as concretions and cavity fillings in sedimentary rocks, and as coatings on them, especially sandstone. It also occurs as iron rust, as scum on stagnant water, and it accumulates around rootlets in soils. Small amounts color limestone, dolomite, clay, shale, sandstone, and gravel. Some sands are firmly cemented by brown or black limonite and look much like iron ore. Clays containing a high percentage of limonite are called ocher.
In some states limonite is mined as an iron ore, and in Illinois it was so used in Hardin County in the middle 1800’s, but deposits are not large enough for profitable use now.
SPHALERITE, zinc sulfide, is a major ore of zinc. It has a resinous luster and a white, yellow, or brown streak. Illinois sphalerite is generally yellow, yellowish brown, reddish brown, or brownish black. It is of medium weight, brittle, can be scratched by a piece of window glass but not by a penny. It is commonly opaque but may be translucent on thin edges.
Sphalerite is mined with galena in northwestern Illinois and in extreme southern Illinois with galena and fluorite. Small crystals occasionally are found in limestones and as crystalline masses in clay-ironstone concretions.
GALENA, lead sulfide, is the principal ore of lead. It is steel gray, heavy, opaque, and has a bright metallic luster, though the shiny surface may be dulled by a coating of lead carbonate. It has a gray or black streak, is soft enough to mark paper, and can be scratched by a penny. The cube-shaped crystals readily break into cubic, right-angled fragments. Probably the most obvious features of the mineral are its bright metallic luster on fresh surfaces, high specific gravity, and cubic cleavage.
At many places galena is argentiferous (silver-bearing), but Illinois galena is relatively unimportant for its silver content. As a source of lead, however, it is an important commercial product of the state.
Scattered pieces of galena are found at many places in Illinois. Some occur in the glacial deposits, others occur as small pockets and as crystals in limestones and geodes. In only two areas of the state are deposits of commercial value. In northwestern Illinois galena occurs in association with sphalerite; in extreme southern Illinois it occurs in association with fluorite and sphalerite.
CONCRETIONS are concentrations of inorganic sedimentary material within other sediments. Minerals that commonly form concretions are silica (in the form of opal, chert, chalcedony, and quartz), calcite, siderite, pyrite, marcasite, and limonite.
Concretions may form either as the sediment around them is forming or after the sediment around them has hardened. They may be formed when water containing dissolved minerals seeps through the sediment or rock and leaves a concentration of mineral matter in a cavity or around a central particle (nucleus) such as the remains of a plant or animal. Portions of rock may also become firmly cemented by such mineral matter.
Concretions range in size from minute particles to objects several feet in diameter. Shapes range from spheres to tubes. Many are globular or lumpy-surfaced, some are smooth. Because concretions generally are harder than the surrounding rock in which they have formed, they do not weather away as readily and may remain after the surrounding material has been eroded.
Concentrations of calcite are found in loess deposits. They may look like bizarre, knobby figurines, and the Germans called them loess kindchen (little children of the loess).
Ironstone concretions, especially common in many Illinois shales, are formed by a local concentration of the mineral siderite (iron carbonate) in the rock. The concretions found in weathered outcrops commonly are partly or entirely weathered to limonite. Some ironstone concretions grow together into odd shapes. Mazon Creek ironstone concretions of northeastern Illinois, world famous for their fossils, are sideritic. The concretions are commonly covered with limonite, the result of oxidation.
Limonite concretions, generally with a high content of clay, silt, or sand, occur in loess, shale, and sandstone.
Concretions of chert and other forms of silica are common in limestones. In many places, because of their greater resistance to weathering, lenses and nodules of chert protrude from the beds.
Pyrite or marcasite occur as concretions or concretion-like masses in some coal beds and in the black shales, sometimes popularly called “slates,” above coal beds. Some other Pennsylvanian clays and shales also contain concretions or coarsely crystalline aggregates of these minerals.
GEODES are roughly spherical bodies that may be filled with layers of minerals, lined with crystals, or both. The outer layer of geodes found in Illinois as a rule is composed of chalcedony, a form of finely crystalline silica.
Geodes differ from concretions in that they form inward from the outer shell, whereas concretions develop outward from a center. Even if geodes have been completely filled by mineral matter, their inward-projecting crystals prove that they formed within a cavity.
In a partly filled cavity, crystals generally are well formed because they grew without being crowded. Some of the best mineral specimens known in Illinois are found as crystal linings in geodes.
Quartz is the most common mineral deposited in geodes, but calcite, aragonite, dolomite, siderite, pyrite, galena, fluorite, and sphalerite also are found.
Geodes ranging in size from less than one inch to a foot or more in diameter can be gathered from streams where they have accumulated as residual boulders after the rock in which they were enclosed has been eroded.
Hollow geodes are the most desirable because they have better crystals. They can be distinguished from solid ones by their comparative lightness of weight.
Geodes are commonly associated with limestone and dolomite, at some places with shale. In Illinois they can be found most easily in the Warsaw Formation in the area of Nauvoo, Hamilton, and Warsaw, but they also occur in other areas and other formations.
Prehistoric animals lived in water, on land, and in the air, and left both direct and indirect evidence of their existence, evidence we now call fossils.
Millions of ancient animals died without leaving a trace, but some, especially those that had hard parts such as shells, bones, or teeth, may be found preserved in rocks much as they were when buried beneath sediment on the floor of an ancient sea. Sometimes only imprints of the outside or fillings of the inside of the shells remain, the original material having been completely dissolved. Footprints of land or amphibious animals, burrows made by clams, or holes made by worms also are fossils.
The animals whose remains are fossilized lived and died while the sediments that contained them were being deposited, and they provide clues to the types of life and climate then existing. Fossils of animals characteristic of a certain time are an index to the age of formations where they occur. For example, if a certain trilobite (an ancient relative of the crayfish and lobster) is known to have lived only during a definite time, then all rocks in which it is found are the same age.
Fossils of animals that lived in the sea are exposed in rocks in many parts of Illinois, especially in quarries, river bluffs, and road cuts.
The oldest fossils found in Illinois are shells of marine animals—snails, corals, crinoids, brachiopods, trilobites, pelecypods (clams), cephalopods, bryozoa, arthropods, and others. The youngest fossils are teeth and bones of prehistoric bison, giant beavers, deer, mammoths and mastodons of the “Ice Age,” and snails found in glacial loess.
PLANT FOSSILS are the remains of prehistoric plants. Woody structures of plants aid preservation just as hard parts of animals do. Leaves and plants without much woody material generally were well preserved only if they were buried quickly in fine, soft sediment.
The most famous Illinois plant fossils are those from the Mazon Creek area in Grundy and Will Counties of northeastern Illinois. The plant material acted as a nucleus around which iron minerals accumulated to form concretions. Many good fossils—of trunks, branches, leaves, and seeds—are found in coals and in shale directly overlying coals. Descendants of “Coal Measures” plants, such as ferns, mosses, and rushes, are still living today, but they no longer thrive as they did in the warm, moist climate of the Pennsylvanian forests.
Some plants of Pennsylvanian age are petrified, and occasionally such trees or stumps are found. Petrified trees are found also in the upper Mesozoic deposits of southern Illinois. Fossils of “Ice Age” plants closely related to forms living at the present time are occasionally found in peat bogs or scattered throughout glacial deposits.
Two keys, one for minerals and one for rocks, briefly present clues that may aid the collector in identifying rocks and minerals found in Illinois. In outline form, the keys are a guide to some of the easily observable properties that various rocks and minerals display.
The rocks and minerals in the school set of “Typical Rocks and Minerals of Illinois” are included, plus other relatively common ones you might find in Illinois. Because of the great diversity of rocks and minerals in this state, the keys are not conclusive. It is therefore suggested you consult other more complete keys (such as that in Dana’s Manual of Mineralogy) when identifying rocks and minerals that are either from other states or are difficult to identify.
The minerals (p. 30-35) are arranged in two groups: 1) those with a metallic luster, and 2) those with a nonmetallic luster. Each group is arranged according to increasing hardness. Other characteristics such as color, streak, cleavage, fracture, and composition are listed.
The rocks (p. 36-39) are arranged according to their reaction to dilute hydrochloric acid applied to a scratched surface. (The acid reacts more readily to powdered material produced by scratching the rock.) After the reaction to acid has been determined, the texture and components of the rock should be noted. Because rocks grade into one another, clear distinctions are not always possible.
| I. METALLIC LUSTER, STREAK COLORED | ||||
|---|---|---|---|---|
| C—color S—streak | H—hardness Cl—cleavage F—fracture | Remarks | Name and composition | |
| A. Hardness not more than 2.5 | ||||
| C—lead gray S—black | H—2.5 Cl—cubic; perfect in 3 directions F—subconchoidal or even | Very heavy; occurs as crystals, grains, or masses; easily identified by color and cleavage | Galena (31) PbS | |
| C—copper red S—metallic, shiny | H—2.5 Cl—none F—jagged | Very heavy; apt to have green coating; distorted or wirelike forms; malleable | Native copper Cu | |
| B. Hardness greater than 2.5 but not greater than 6.5 | ||||
| C—yellow-brown to black S—yellow-brown | H—5.5 (may be as low as 1) Cl—none F—uneven | In earthy masses; coloring material in many sandstones, conglomerates, and soils; often mixed with and difficult to distinguish from goethite and other iron minerals | Limonite (29) FeO(OH)·H₂O | |
| C—brassy yellow S—greenish black | H—6 Cl—poor F—conchoidal to uneven | As compact masses, grains, cubes, and in 8- and 12-sided crystals; commonly associated with coal, and with lead-zinc ores of northwestern Illinois | Pyrite (28) FeS₂ | |
| C—pale brassy yellow to silver white S—greenish gray | H—6 Cl—poor F—uneven | As fibrous, radiating, tabular, and cocks-comb crystals or compact masses; usually lighter colored than pyrite, but difficult to distinguish from pyrite; associated with coal, and with lead-zinc ores of northwestern Illinois | Marcasite FeS₂ (28) | |
| II. NONMETALLIC LUSTER, STREAK WHITE | ||||
| A. Hardness not greater than 2 (can be scratched by fingernail) | ||||
| C—usually white but may be almost any color | H—2 Cl—perfect in one direction, less perfect in two others | Commonly found in Illinois as twinned or needle-shaped crystals in weathered shales containing pyrite and calcium carbonate | Gypsum (26) CaSO₄·2H₂O | |
| C—white or a shade of green | H—2 | As needle-shaped crystals or powdery coating on pyrite or marcasite; has an astringent taste | Melanterite FeSO₄·7H₂O | |
| B. Hardness greater than 2 but not greater than 3 (Can be scratched by a penny) | ||||
| C—colorless, silver white, gray, brown | H—2-2.5 Cl—perfect in one direction | In scales or “books”; in splits into thin sheets; common in sandstones, shales, and in igneous and metamorphic rocks | Muscovite (white mica) (23) (OH)₂KAl₂ AlSi₃O₈ | |
| C—brown or black | H—2.5-3 Cl—perfect in one direction | As scales or “books”; splits into thin sheets; common in igneous and metamorphic rocks but not in sedimentary rocks such as sandstone or shale | Biotite (23) (black mica) (OH)₂K(Mg,Fe)₃ AlSi₃O₈ | |
| C—colorless, white, gray, and various tints | H—3 Cl—perfect in three directions, not at right angles (rhombohedral) | Common mineral; effervesces vigorously in cold acid; occurs in many crystal forms and as fibrous, banded, and compact masses; chief mineral in limestones | Calcite (24) CaCO₃ | |
| C—white, gray, red, or almost any color | H—3 Cl—perfect in one direction, less perfect in two other directions | Very heavy; commonly in tabular crystals united in diverging groups, as laminated or granular masses; associated with fluorite in southern Illinois | Barite BaSO₄ | |
| C. Hardness greater than 3 but not greater than 5 | ||||
| (Cannot be scratched by penny; can be scratched by knife) | ||||
| C—white, gray, light yellow | H—3.5 Cl—in one direction F—uneven | Relatively heavy; effervesces in acid; associated with fluorite and barite in southern Illinois but is not abundant | Witherite BaCO₃ | |
| C—white, pink, gray, or light brown | H—3.5 Cl—perfect in three directions, not at right angles (rhombohedral) | In grains, rhombohedral crystals and cleavable or granular masses; effervesces slowly in cold acid when powdered, more vigorously in warm acid; principal mineral in rock called dolomite | Dolomite CaMg(CO₃)₂ | |
| C—colorless, white, gray, grayish black | H—3.5 | In fibrous or compact masses or may be in orthorhombic crystals as a coating on galena; very heavy; effervesces in acid; formed by alteration of galena | Cerussite PbCO₃ | |
| C—brown to gray S—usually white but may tend toward brown when weathered | H—3.5 Cl—in three directions not at right angles (rhombohedral) slightly curved surfaces | In fibrous or botryoidal masses or rhombohedral crystals; effervesces in hot acid | Siderite FeCO₃ | |
| C—yellow, yellow-brown to almost black S—light yellow to brown | H—3.5 Cl—parallel to dodecahedral faces; in six directions | In crystals, in fibrous or layered masses; associated with galena in northwestern Illinois, with fluorite and galena in southern Illinois | Sphalerite ZnS (30) | |
| C—colorless, white, yellow, purple, green, blue | H—4 Cl—perfect, parallel to octahedral faces; in four directions | In cubes and cleavable masses; many colors; mined in Hardin and Pope counties | Fluorite (25) (Fluorspar) CaF₂ | |
| C—white, tinted yellow, blue, or green | H—5 | As crystalline incrustations or in earthy or compact masses; associated with fluorite-sphalerite ores in southern Illinois, with galena and sphalerite in northwestern Illinois | Smithsonite ZnCO₃ | |
| D. Hardness greater than 5 but not greater than 7 | ||||
| C—white, green, brown, black | H—5-6 Cl—in two directions intersecting at about 60° and 120° | In long, slender 6-sided crystals; cleavage angle important in differentiating from pyroxenes; common in metamorphic and some igneous rocks | Amphibole Group (Mg,Fe,Ca)₇(Si₈O₂₂)(OH)₂ (may also contain Na or Al) | |
| C—gray, dark green, black, dark brown, bronze | H—5-6 Cl—in two directions intersecting at about 90° | Crystals short, stout, and 8-sided; cleavage angle important in differentiating from amphiboles; common in igneous and some metamorphic rocks | Pyroxene Group (Mg,Ca,Fe)₂(Si₂O₆) | |
| C—white, gray, pink, light blue, green | H—6 Cl—in two directions nearly at right angles | As crystals, cleavable masses and grains; common in igneous and metamorphic rocks, also in stream gravel and sand; many varieties | Feldspar Group (22) K, Na, Ca, Ba (Al, Si)₄O₈ | |
| C—white when pure; may be colored by impurities | H—7 Cl—none F—conchoidal | Finely crystalline variety of quartz; botryoidal or concretionary masses; lining in geodes | Chalcedony SiO₂ | |
| C—colorless, white, or almost any color | H—7 F—conchoidal | Most abundant mineral; occurs in 6-sided crystals capped by pyramids, in grains or masses; principal mineral in sandstone, also abundant in igneous and metamorphic rocks; is a variety of silica | Quartz (21) SiO₂ | |
| C—red | H—7 F—conchoidal | A variety of quartz usually colored red by hematite inclusions; common in glacial and river sand and gravel found along Lake Michigan shores and in the Mississippi River | Jasper SiO₂ | |
| C—many; arranged in bands | H—7 F—conchoidal | Cloudy banded variety of silica; widely used as semi-precious stones. Onyx and silicified wood are forms of agate; found in glacial gravels and upper Mesozoic sediments in southern Illinois | Agate SiO₂ | |
| E. Hardness greater than 7 (cannot be scratched by quartz) | ||||
| C—red, brown, yellow, green, black, white | H—7.5 Cl—poor F—even | Irregular grains or masses; sometimes as 12-, 24-, and 36-sided crystals; abundant in glacial sands and Lake Michigan beach sands; common in metamorphic rocks | Garnet Group (Ca,Mn,Fe,Mg)₃(Al,Cr)₂(SiO₄)₃ | |
1. Hammer (bricklayer’s) with one chisel or pick head.
2. Cold chisel about 6 inches long with an edge about ½-inch wide.
3. Dilute hydrochloric (muriatic) acid (10 percent solution) in a dropper bottle for testing the presence of carbonate minerals. Mark the bottle POISON. If acid is spilled on skin or clothing, wipe immediately and, if possible, rinse with water.
4. Magnifying glass or hand lens—10 power is probably most useful.
5. Hardness testers—penny, square of window glass, pocket knife, or nail.
6. Streak plate—piece of unglazed white porcelain (such as the back of a tile) for testing the color of the streak of minerals.
7. Notebook and pencil for keeping records of the locality and bed from which specimens are collected.
8. Collecting bag—a musette bag, a knapsack, or similar bag of strong material.
9. Heavy gloves and goggles to protect hands and eyes.
10. Labels and wrappings. Field identification of specimens may be written on adhesive tape and attached to the specimen or on a slip of paper enclosed in the wrapping. Newspaper, brown paper, or paper bags can be used for wrapping specimens. Label the outside of the wrapped specimen too. Take only the best specimens home with you. Trim specimens to hand size (about 2 by 3 inches).
All specimens should be labeled with the following information: name of mineral or rock type, where found, collector’s name, and date. As your collection grows, you may want to set up a system of cataloging. List specimens and assign a number to each one. Place a small amount of white enamel on a corner of each specimen; when the enamel dries, number the sample with India ink; coat number with lacquer. Corresponding numbers should be entered on your list of specimens.