Rocks and Minerals
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| Type | Earth Science | ||||||||
| Category | Study | ||||||||
| Description | Teams will demonstrate their knowledge of rocks and minerals. | ||||||||
| Event Information | |||||||||
| Latest Appearance | 2023 | ||||||||
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Rocks and Minerals is an identification event for the 2022 and 2023 seasons in both Division B and Division C in which teams use their knowledge of rocks and minerals to identify pictures/specimens and complete a written test.
The official Rocks and Minerals List for 2018 includes specific rocks and minerals covered in the event. The 2018 identification list can be found here.
General Information
In Rocks & Minerals, teams identify rocks and minerals from the official list and answer questions about them. This competition is usually in a station format. Competitors are allowed to bring one 3-ring binder of any size. In previous years teams were allowed to bring a commercially published field guide; as of the 2017 season this is no longer allowed. This was changed in the 2022 season, one field guide per team is allowed again.
Rocks
There are three classifications of rocks: igneous, metamorphic, and sedimentary. Any type of rock can be transformed into another kind. Igneous rocks are created from solidified magma (rock that has been melted inside the earth), sedimentary rocks are created when smaller bits of rock or sand are cemented together, and metamorphic rock are formed when other types of rocks are subjected to heat and pressure.
Igneous Rocks
There are two main classifications of igneous rocks: intrusive and extrusive rocks.
Intrusive rocks harden slowly beneath the surface of the earth, and often form large mineral crystals within the rock. Granite is a good example of an intrusive rock. Porphyritic intrusive rocks have large crystals embedded in a matrix of smaller crystals. Pegmatite is the only porphyritic rock on the Science Olympiad list.
Extrusive rocks harden quickly during a volcanic eruption and are usually smooth-grained. Basalt is the most common form of extrusive rock.
| Name | Classification | Description |
|---|---|---|
| Andesite | Extrusive | Usually blackish-brown, sometimes greenish. Papier-mache look.Contains less than 5% quartz. |
| Basalt | Extrusive | Very dark, often black. Often contains phenocrysts of feldspars, olivine, and other dark minerals |
| Diorite | Intrusive | Dark gray to blackish gray, mottled. Evenly speckled with dark and light minerals, salt-and-peppery look. |
| Gabbro | Intrusive | Gray or light green, very coarse-grained. |
| Granite | Intrusive | Crystals of feldspar (pink or red), mica (dark brown or black), and quartz (clear pink, white, or black).Coarse-grained. |
| Obsidian | Extrusive | Shiny black.Volcanic glass, has a conchoidal fracture (see explanation of cleavage and fracture below) Be careful |
| Pegmatite | Intrusive | Same composition as granite but has very large, usually light crystals. |
| Pumice | Extrusive | Very light gray. Also volcanic glass, but very light and bubbly. Only rock that floats. |
| Rhyolite | Extrusive | Usually light grayish-pink. Made of the same minerals as obsidian and pumice, but did not cool as quickly. |
| Scoria | Extrusive | Dark gray, red, or black. Composed of basalt that cooled very quickly with trapped air, so it is bubbly-looking. |
Sedimentary Rocks
Sedimentary rocks occur when smaller bits of rock and sand are cemented together. Sedimentary rocks are either clastic or organic.
Clastic rocks, like sandstone, form from other rocks and minerals.
Organic rocks, like limestone and coal, form from the bodies or shells of organisms.
The Wentworth scale (also known as the Udden-Wentworth scale) is a logarithmic scale used in the United States that sorts rocks by grain size. It's typically not mentioned on regional tests, but may be found on the state level exam. The lower the value on the Wentworth scale, the larger the grain size. The formula for the Wentworth scale is
where [math]\displaystyle{ \phi }[/math] is the rating on the scale, [math]\displaystyle{ D }[/math] is the diameter of the grain in millimeters, and [math]\displaystyle{ D_0 }[/math] is a reference diameter, equal to 1 mm.
| Name | Classification | Description |
|---|---|---|
| Anthracite Coal | Organic | 93-98% pure carbon. Shiny, scaly black. Conchoidal fracture. Can be used like black chalk. |
| Arkose | Clastic | Formed mostly from feldspar. Gray or pink. Coarse grained, looks like sandstone with redder tint (mostly quartz). |
| Bituminous Coal | Organic | 50-65% carbon Black. Not very shiny. Well-jointed, splinters under pressure. Hardness: 2. |
| Breccia | Clastic | Conglomerate of sharp, angular fragments. Often forms after rock slides. |
| Conglomerate | Clastic | Conglomerate of smooth, rounded fragments. Has the largest grain sizes. Often forms in riverbeds. |
| Coquina | Organic | Conglomerate of limestone shell fossils that are poorly cemented. * Clastically formed organic fragments. |
| Diatomite | Organic | Light tan, cream, or white. Extremely lightweight, lighter even than chalk. Called "fossil flour" because it easily falls apart into flour-like dust. |
| Dolomite/Dolostone | Clastic | Light gray, yellowish, pinkish. Contains a mixture of limestone, but at least 50% dolomite (mineral). Often contains fossils. |
| Lignite Coal | Organic | Coal that retains fibrous, woody structure. Less than 50% carbon. |
| Limestone | Clastic | Composed of the fossilized shells of marine organisms. Chalk: White, soft, porous. Crystalline: white, hard, crystalline. Fossiliferous: fossil structures can still be seen in rock. Oolitic: formed from small, round organisms that can still be seen individually. Travertine: Color-banded, crystalline, often fibrous or concretionary. |
| Sandstone | Clastic | Even, medium-sized quartz grains. Color variable, often tan, pink, or red. |
| Shale | Clastic | Very small, microscopic particles. Soft, and splits into plates. Brown or black. |
Metamorphic Rocks
Metamorphic rocks are composed of other rocks that have been subjected to heat and pressure. These rocks often bear little resemblance to their parent rocks.
| Name | Parent Description | Grain | Color and Foliation | Metamorphism |
|---|---|---|---|---|
| Gneiss | Can be formed from almost any other rock | Medium to coarse grained. | White or gray, but foliated with dark rock. Must be less than 50% foliated. | High grade metamorphism |
| Marble | Calcite or limestone | Fine to medium grained. | White, can be patched with green, gray, brown, or red. | The metamorphism of limestone or dolomite. |
| Phyllite | Slate | Very fine grains, wavy bands. | Light, silvery-gray to lead-gray. Silky sheen | |
| Schist | Almost any rock | Garnet Schist: Contains fairly large garnet inclusions. Mica Schist: Very shiny because of diorite inclusions. | Silvery-gray, banded, wavy. Must be more than 50% foliated with dark rock. | |
| Quartzite | Pure sedimentary rocks | Fairly small particles. | White to patchy gray. Can range from sugary green to gray to pink. | The metamorphism of sandstone. |
| Slate | Shale | Very small particles. | Dark gray, shiny | Low grade Metamorphism. |
Rock Cycle
Transition to Igneous:
When rocks are pushed deep under the Earth's surface, they may melt into magma. If the conditions no longer exist for the magma to stay in its liquid state, it will cool and solidify into an igneous rock. A rock that cools within the Earth is called intrusive or plutonic and will cool very slowly, producing a coarse-grained texture. As a result of volcanic activity, magma (which is called lava when it reaches Earth's surface) may cool very rapidly while being on the Earth's surface exposed to the atmosphere and are called extrusive or volcanic rocks. These rocks are fine-grained and sometimes cool so rapidly that no crystals can form and result in a natural glass, such as obsidian. Any of the three main types of rocks (igneous, sedimentary, and metamorphic rocks) can melt into magma and cool into igneous rocks.
Secondary Changes:
Epigenetic change (secondary processes) may be arranged under a number of headings, each of which is typical of a group of rocks or rock-forming minerals, though usually more than one of these alterations will be found in progress in the same rock. Silicification, the replacement of the minerals by crystalline or crypto-crystalline silica, is most common in felsic rocks, such as rhyolite, but is also found in serpentine, etc. Kaolinization is the decomposition of the feldspars, which are the most common minerals in igneous rocks, into kaolin (along with quartz and other clay minerals); it is best shown by granites and syenites. Serpentinization is the alteration of olivine to serpentine (with magnetite); it is typical of peridotites, but occurs in most of the mafic rocks. In uralitization, secondary hornblende replaces augite; chloritization is the alteration of augite (biotite or hornblende) to chlorite, and is seen in many diabases, diorites and greenstones. Epidotization occurs also in rocks of this group, and consists in the development of epidote from biotite, hornblende, augite or plagioclase feldspar.
Transition to Metamorphic:
Rocks exposed to high temperatures and pressures can be changed physically or chemically to form a different rock, called metamorphic. Regional metamorphism refers to the effects on large masses of rocks over a wide area, typically associated with mountain building events within orogenic belts. These rocks commonly exhibit distinct bands of differing mineralogy and colors, called foliation. Another main type of metamorphism is caused when a body of rock comes into contact with an igneous intrusion that heats up this surrounding country rock. This contact metamorphism results in a rock that is altered and re-crystallized by the extreme heat of the magma and/or by the addition of fluids from the magma that add chemicals to the surrounding rock (metasomatism). Any pre-existing type of rock can be modified by the processes of metamorphism.
Transition to Sedimentary:
Rocks exposed to the atmosphere are variably unstable and subject to the processes of weathering and erosion. Weathering and erosion break the original rock down into smaller fragments and carry away dissolved material. This fragmented material accumulates and is buried by additional material. While an individual grain of sand is still a member of the class of rock it was formed from, a rock made up of such grains fused together is sedimentary. Sedimentary rocks can be formed from the lithification of these buried smaller fragments (clastic sedimentary rock), the accumulation and lithification of material generated by living organisms (biogenic sedimentary rock - fossils), or lithification of chemically precipitated material from a mineral bearing solution due to evaporation (precipitate sedimentary rock). Clastic rocks can be formed from fragments broken apart from larger rocks of any type, due to processes such as erosion or from organic material, like plant remains. Biogenic and precipitate rocks form from the deposition of minerals from chemicals dissolved from all other rock types.
Minerals
By definition, minerals must have definite chemical and crystal structures. There are a large variety of minerals, many of which are very common. In order to understand minerals, it is helpful to understand basic chemistry and the periodic table (this is not covered on this page, but can be found in any chemistry book). Each mineral can be classified by ten different characteristics: group, formula, color, streak, luster, crystal structure, cleavage, fracture, hardness, and specific gravity.
Definitions
- Group
Minerals are organized into groups based on their chemical makeup. Native elements are composed of a single, pure element; Sulfides contain sulfur, arsenic, tellurium, or selenium; Oxides and Hydroxides contain oxygen compounds; Halides contain sodium, chlorine, fluorine, iodine, or bromine; Carbonates and Borates contain the carbonate or borate groups; Sulfates contain the sulfate group; Phosphates, Arsenates, and Vanadates contain one of those chemical groups; Silicates contain the elements silicon and oxygen in some proportion.
- Formula
Each mineral has a definite chemical composition. For example, copper difluoride is CuF2. Understanding the naming of formulas may require reviewing a chemistry textbook.
- Color
Color is not a reliable way to identify minerals. Some minerals can be any color under the sun. While color can sometimes be useful, do not rely on it!
- Streak
Streak is the color when a rock is rubbed across an unglazed piece of porcelain. Streak is much more useful than color because a mineral always has the same streak, but it still has its limits because minerals harder than the streak plate will scratch the streak plate instead of producing powder.
- Luster
A mineral’s luster is the way it reflects light. Descriptions of luster are very subjective but are sometimes useful. Common types of luster are vitreous (glassy), adamantine (brilliant or gem-like), resinous (resin-like), greasy, pearly, waxy, and silky.
- Crystal Structure
- Crystal structure is the basic shape of a mineral as it grows. A good mineral book, like the Peterson Field Guide, will describe the different crystal structures. Here are some of them:
Isometric - Three axes of symmetry, all at right angles to one another, and all of equal lengths. Sometimes called cubic.
Tetragonal - Three axes of symmetry, all at right angles to one another, two of the same length and one shorter.
Hexagonal (Trigonal) - Four axes of symmetry; three are of equal length and lie in the same plane at 120 degrees, the other can be any length and lies at right angles to the others. (Note: Trigonal is sometimes considered to be separate from hexagonal.)
Orthorhombic - Three axes, all at right angles to one another, of three different lengths.
Monoclinic - Three unequal axes, two at right angles, and the other inclined.
Triclinic - Three unequal axes, none of which are at right angles to any others.
- Cleavage
When a mineral has the tendency to break along smooth, flat surfaces, it has cleavage. If the break is perfectly smooth and shiny, it is said to have perfect cleavage. Cleavage can also be described as good, distinct, or poor.
- Fracture
Fracture is described as the way a mineral breaks (not along a cleavage plane). It can be uneven, hackly (sharp, jagged surface like broken metal), splintery, or conchoidal (shell-like).
- Hardness
The Moh’s Hardness Scale, which is used by most mineral collectors, is based on the hardness of other minerals. It is on a scale of one to ten, ten being the hardest. To test two minerals against each other, try to scratch each mineral with the other in an inconspicuous place. If they both scratch each other, they have the same hardness. If only one causes a scratch, it is the hardest. Or, common objects can be used (such as pennies and nails) to see if they scratch or can be scratched by a mineral.
Hardness Mineral or Common Object 1 Talc 2 Gypsum 2.5 Fingernail 3 Calcite 3 Copper penny 4 Fluorite 5 Apatite 5.5 Knife blade 6 Feldspar 6 Window glass 7 Quartz 7 Steel file 8 Topaz 9 Corundum 10 Diamond
- Specific Gravity
Specific gravity (SG) is a measure of how dense a mineral is. It compares the mass of one gram of the mineral to the mass of one gram of water. So a mineral with a SG of 4.5 is 4.5 times as heavy as water. With practice, it can be determined whether a mineral specimen is "light" (usually less than 3.5) or "heavy" (greater than 4) just by holding it. Specific gravity can be helpful in detecting metallic minerals (which are usually heavier), or cases where a mineral is unusually heavy. For example, galena is a gray, metallic mineral with a high lead content, and it is noticeably heavy. Specific gravity is especially useful in the case of barite, a white mineral which is unusually heavy because it contains the heavy metal barium, but does not look metallic at all.
This page does not list the characteristics of every mineral; however, more information can be found in any good mineral identification handbook. Learning every characteristic of every mineral is possible, but it is a good idea to only try and memorize the one distinguishing characteristic of each mineral. Short descriptions that help remembering minerals are also a good idea.
Mineral Name Description
| Name | Hardness | SG | Streak | Color | Group | Crystal System |
|---|---|---|---|---|---|---|
| Talc | 1 | 2.58-2.83 | White | Light to gray, green | Silicates | Monoclinic |
| Graphite | 1-2 | 2.1-2.3 | Gray | Grey | NE | Trigonal/ Hex |
| Bauxite | 1-3 | 2.3-2.7 | White | Yellow, brown | Oxides | N/A |
| Sulfur | 1.5-2.5 | 2-2.1 | White | Yellow | NE | Orthorhombic |
| Halite | 2 | 2.1-2.2 | White | Numerous | Halides | Cubic |
| Gypsum | 2 | 2.32 | White | Light medium | Sulfates | Monoclinic |
| Kaolinite | 2-2.5 | 2.6-2.63 | White | Light, medium | Silicates | Triclinic |
| Ulexite | 2.5 | 1.96 | White | Colorless | Borates | Triclinic |
| Galena | 2.5 | 7.58 | Lead-gray | Lead gray | Sulfides | Cubic |
| Lepidolite | 2.5-3 | 2.8-3.3 | Colorless | Pink, purple, med. | Silicates | Monoclinic |
| Copper | 2.5-3 | 8.9 | Copper-red | Copper or green | NE | Cubic |
| Silver | 2.5-3 | 10.5 | Silver-white | Silver | NE | Cubic |
| Gold | 2.5-3 | 19.3 | Golden-yellow | Yellow | NE | Cubic |
| Biotite | 2.5-4 | 2.7-3.4 | Colorless | Dark | Silicates | Monoclinic |
| Muscovite | 2.5-4 | 2.77-2.88 | Colorless | Light | Silicates | Monoclinic |
| Calcite | 3 | 2.71 | White grayish | Light medium | Carbonates | Trigonal/ Hex |
| Bornite | 3 | 5-5.1 | Gray-black | Dark/ Blue | Sulfides | Cubic |
| Celestite | 3-3.5 | 3.96-3.98 | White | Light | Sulfates | Orthorhombic |
| Barite | 3-3.5 | 4.5 | White | Light medium | Sulfates | Orthorhombic |
| Dolomite | 3.5-4 | 2.85 | White | Light | Carbonates | Trigonal/ Hex |
| Aragonite | 3.5-4 | 2.94-2.95 | White | Many | Carbonates | Orthorhombic |
| Azurite | 3.5-4 | 3.77-3.78 | Pale blue | Deep blue | Carbonates | Monoclinic |
| Sphalerite | 3.5-4 | 3.9-4.1 | Colorless-brown | Num. Esp. black | Sulfides | Cubic |
| Malachite | 3.5-4 | 4 | Pale green | Deep green | Carbonates | Monoclinic |
| Chalcopyrite | 3.5-4 | 4.3-4.4 | Green-black | Brassy yellow | Sulfides | Tetragonal |
| Fluorite | 4 | 3.1-3.3 | White | Numerous | Halides | Cubic |
| Apatite | 5 | 3.1-3.2 | White | Many esp. green | Phosphates | Trigonal/ Hex |
| Goethite | 5-5.5 | 3.3-4.3 | Orange brownish | Black-brown light | Hydroxides | Orthorhombic |
| Tremolite | 5-6 | 2.9-3.2 | White | Many esp. white | Silicates | Monoclinic |
| Hornblende | 5-6 | 3.28-3.41 | White gray | Dark esp. green | Silicates | Monoclinic |
| Hematite | 5-6 | 5.26 | Brown-red | Brown red, black | Oxides | Trigonal/ Hex |
| Sodalite | 5.5-6 | 2.14-2.4 | Colorless | Many esp. blue | Silicates | Cubic |
| Augite | 5.5-6 | 3.23-3.52 | Gray-green | Dark esp. Black | Silicates | Monoclinic |
| Opal | 5.5-6.5 | 1.9-2.3 | White | Many esp. dark | Silicates | N/A |
| Rhodonite | 5.5-6.5 | 3.57-3.76 | White | Red pink | Silicates | Triclinic |
| Magnetite | 5.5-6.5 | 5.2 | Black | Black | Oxides | Cubic |
| Amazonite | 6-6.5 | 2.55-2.63 | White | Medium esp. green | Silicates | Triclinic |
| Feldspar | 6-6.5 | 2.55-2.63 | White | White red | Silicates | Monoclinic |
| Albite | 6-6.5 | 2.6-2.63 | White | Many Esp. Light | Silicates | Triclinic |
| Pyrite | 6-6.5 | 5 | Green-black | Pale yellow | Sulfides | Cubic |
| Epidote | 6-7 | 3.35-3.5 | Colorless-grayish | Dark or yellowish | Silicates | Monoclinic |
| Olivine | 6.5-7 | 3.27-4.32 | Colorless | Green brown | Silicates | Orthorhombic |
| Almandine (garnet) | 6.5-7.5 | 4.1-4.3 | White | Dark esp. brown | Silicates | Cubic |
| Quartz | 7 | 2.65 | Colorless-white | Numerous | Silicates | Trigonal/ Hex |
| Tourmaline Group | 7-7.5 | 3-3.2 | Colorless | Medium | Silicates | Trigonal/ Hex |
| Staurolite | 7-7.5 | 3.65-3.83 | Colorless-grayish | Dark | Silicates | Orthorhombic |
| Beryl | 7-8 | 2.6-2.9 | White | Numerous | Silicates | Trigonal/ Hex |
| Topaz | 8 | 3.49-3.57 | Colorless | Numerous | Silicates | Orthorhombic |
| Corundum | 9 | 4-4.1 | White | Numerous | Oxides | Trigonal/ Hex |
| Diamond | 10 | 3.52 | White | Numerous | NE | Cubic |
| Name | Hardness | SG | Streak | Color | Group | Crystal Shape |
More Rocks and Minerals Descriptions
Albite - white, tan, or cream feldspar
Almandine - dark red, garnet
Amazonite - bright green feldspar
Apatite - usually green or purple, but can be almost any color
Aragonite - white, powdery variety of calcite. can often form amber colored hexagonal crystals
Augite - one of the approximately six minerals on the list that look like nondescript black rocks; however, it has a greenish tinge and cleavage at a right angle that set it apart a little
Azurite - always blue (one of those minerals where color can be depended on), with a blue streak
Bauxite - tan rock with orange, white, and prown pisoliths of aluminum, causing light weight, formed from weathering of feldspars
Barite - white and kind of platy, but very heavy because it contains barium. can form rosettes
Beryl - the cheap specimens usually seen in Science Olympiad are mostly light green and opaque; often have hexagonal crystal; aquamarine and emerald
Biotite - black mica – thin and platy; comes off in thin sheets
Bornite - "Peacock Copper;" has a dark, purplish-blue tarnish, also called Peackock Tarnish; chalcopyrite, which looks almost the same, tarnishes purple, orange, yellow, and red
Calcite - looks almost like fluorite and can be any color, but it is a little softer and it has a more rhombus like shape. It also bubbles in hydrochloric acid (hcl), but most people do not have that lying around to test rocks with
Celestite - usually a soft, translucent white or blue
Chalcopyrite - very brassy yellow, tarnishes bright red, purple, yellow, and orange
Copper -copper color, see the green tarnish
Corundum - very hard reddish or purplish rock, very hard and often has small column-like opaque crystals, rubies and sapphires
Diamond - adamantine luster, comes in various lighter colors, hardest mineral
Dolomite - thin, platy cream-colored crystals; sometimes there are dark specks embedded between the crystals
Epidote - mostly greenish-yellow and grainy, but can be almost any shade of green; often confused with olivine; described as "pistachio"
Feldspar - kind of a salmon-pink color; has a very distinctive luster
Flourite - almost any color; hard to distinguish from calcite, but it is a little harder; usually has dipyramidal or cubic structure
Galena - has perfect cubic cleavage and is very heavy, made of lead sulfide and is an important lead ore
Goethite - another "black rock", sometimes has a slightly iridescent tarnish, though, has been described as an "ugly brownish orange-black rock"
Gold - gold colored, do not confuse with pyrite, typically smoother than pyrite, generally forms nuggets while pyrite usually forms cubic crystals
Graphite - silver, shiny, soft, and leaves dark smudges on hands, used for pencil lead.
Gypsum - looks like any number of transparent colorless minerals, but luckily gypsum is very soft and easily scratched with a fingernail; alabaster gypsum is white and opaque, satin-spar is white and fibrous, and selenite is transparent
Halite - rock salt; about the color and hardness of selenite gypsum; it has nice cubic crystals, though, and it can usually be identified it from that; tasting specimens is against the rules in science olympiad, but smelling them is not and salt has a distinct smell along with a greasy feel
Hematite - hematite will either be black and shiny, dark gray and dull, or rusty red. Its most distinctive feature is it is cherry red streak, but it also has one other interesting property. It is almost always cool to the touch, much more than magnetite (which it looks like).
Hornblende - black with short stubby crystals, and usually striated lengthwise
Kaolinite - looks like chalk, but is actually clay; usually white and orange
Lepidolite - pink or lilac color; also has darker purple dots, called lamellae; a type of mica so it is sometimes found in sheets
Magnetite - looks a lot like hematite, except it is magnetic; it also has a gray or black streak - hematite’s streak is cherry-red
Malachite - this mineral is easy because it is always green, with a green streak; often found with azurite
Muscovite - white, yellow, or tan mica-thin and platy
Olivine - usually light green or yellowish-green, transparent specimens are called peridot
Opal - precious opal is iridescent, but most opal is white and opaque with a greasy or waxy luster; usually amorphous crystals
Pyrite - metallic fool’s gold, often found in cubic or hexagonal crystals. It has a blackish green streak. Distinguished from gold by greater hardness, lower specific gravity, rougher surface, and tendency to form cubic crystals as opposed to nuggets
Quartz - fairly hard, no cleavage; agate is often grey or brown and is banded, onyx is a black variety of agate, amethyst is purple and transparent, chalcedony is waxy, transparent grey and usually found in bulbous masses, chert/flint is white/black and noncrystalline with a marked conchoidal fracture, citrine is yellow or orange and transparent, crystal is colorless and transparent, jasper is orange or red and opaque, milky is crystalline but white or light tan, rose is pale pink
Rhodonite - comes in all shades of pink and red; usually massive, but sometimes crystalline
Silver - metallic silver color; pure form has the highest reflectiveness of any element, but it is usually tarnished; this tarnish is silver sulfide and appears dull, dark gray
Sodalite - always blue, but usually a very dark, mottled blue; its darker color and colorless streak tell it apart from azurite
Sphalerite - can be almost any color, but usually yellowish, tan, or reddish. It sometimes comes in crystals, but it can be massive, too when it is usually a dark brown; has a resinous luster
Staurolite - almost always forms short, prismatic crystals; usually brown, and sometimes forms cruciform twins
Sulfur - always some shade of yellow and it gives off a sulfurous odor when rubbed
Talc - very soft, often light green, white, or grey and feels very waxy
Topaz - extremely variable color but usually comes in well-formed prismatic crystals, a light colored gem
Tourmaline - also extremely variable when it comes to color, but it often comes in long prismatic crystals with vertical striations on it is surface; pleochroric (same crystal appears different color depending on viewing angle)
Tremolite - usually comes in small, bladed crystals, light-colored and sometimes transparent, commercially was used as asbestos
Ulexite - almost always white, and looks like a densely-packed bundle of white threads; opaque in one direction and conducts light in the other; fiber-optic abilities gave it the nickname "T.V. rock"
Bowen’s Reaction Series
Bowen’s Reaction Series is the work of Norman Bowen, a petrologist who conducted experiments with heating rock material at different temperatures and analyzing results. The reaction series helps explain why certain minerals are commonly found together, while others combinations are rare.
The series is broken in two branches, continuous and discontinuous For the continuous branch, the series explains that at the highest temperatures, calcium-rich Plagioclase will form. As temperatures become cooler, sodium-rich Plagioclase will form, and Orthoclase, Muscovite, and Quartz will follow. For the discontinuous branch, the series says that Olivine will form at the highest temperatures, followed by Pyroxene, Amphibole, and Biotite. After Biotite, the branch produces Orthoclase, Muscovite, and Quartz, like the continuous branch describes.
The reaction series also helps explain why certain minerals are only found in certain types of igneous rocks. As olivine and pyroxene form at higher temperatures, they are more likely to be found in ultramafic and mafic rocks, as compared to felsic rocks. Conversely, quartz is found largely in felsic rocks due to forming at the lower temperatures and crystallizing later.
Picking a Field Guide
It is advisable to use a binder over a field guide, since not only can a binder be organized with one’s own discretion, but also preparing sheets for a binder can help with learning facts (plus it is great for general geology/petrology/mineralogy notes). However, for those who prefer field guides, here is a guide by SciOly user quizbowl on picking one:
"quizbowl's guide to field guides"
Simon and Schuster - Definitely the best one of them all. Okay pictures, a lot of information, and has great notes in the start of each section. I think it is quite concise and efficient - very reliable. Not the easiest read, but definitely numero uno. Hands down
Peterson - A not-so-close second, but a clear silver medalist here. Not as informative as Simon and Schuster, but does have nice pictures and good ID tips. I like the layout. Good backup Audubon - This guide is pretty good, but rather unorganized. There is a lot of information, but a lot of it is crammed too much and unimportant. The pictures are usually good, but the information was a bit outdated even in the most recent version Smithsonian - This one is great for learning how to identify the rocks, but once you get past that, its use and value drops considerably. Not a terrible start, though The Complete Guide to Rocks and Minerals - A bit similar to that of Smithsonian, but at least goes a bit in depth. Seems quite large to carry around while running to stations - might as well just use a binder So, in short, if you’re just starting off, try Peterson or Smithsonian. Once you’ve mastered some of the general basics, try your hand at Simon and Schuster. But why use them when you can have a lovely binder? (Tip: it is perfectly okay to splice pages of your field guide into your binder) |
Advice
- Speed is the key: Rocks & Minerals is a very fast-paced event, and it is important to be able to find information quickly because most stations have multiple tasks in a short time period, so organization is very important. Less may seem like more, but the advantages comes in knowing the binder and the material well. If the amount of information in the binder is minimized there's less information to sort through, but key information can also be left out. As a rule of thumb, keep it travel-sized (a one-inch binder should be plenty, and a fairly good book will do)
- Do not just read the wiki page and expect it to mention everything. Get a couple of good books and get to know them really, really well. Eventually the book will not be needed for basic identification, but it is always good to keep them around just in case.
- The Peterson Field Guide to Rocks and Minerals is a recommended field guide by a Rocks and Minerals veteran. The Audubon book is also recommended (the field guide, not the pocket guide), as is the Eyewitness Handbook
- Buy or borrow a college book on geology or mineralogy. There are also a lot of good internet resources. [www.minerals.net] is a good place to start with good descriptions of minerals and a lot of nice links.
- Include multiple images of each specimen in the binder, and work with actual specimens if possible. Knowing how a specific rock or mineral looks will be more advantageous than having to flip through the binder to identify specific rocks or minerals.