Rocks and Minerals

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Rocks and Minerals
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Division B Champion Muscatel Middle School
Division C Champion William P. Clements High School

Rocks and Minerals is an identification event in which teams will use their knowledge of rocks and minerals to identify pictures and complete a written test.

The event will be held in the 2013-2014 season.

See the Official Rock and Mineral List for specific rocks and minerals that will be covered.

Contents

General Information

In Rocks & Minerals, teammates 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 and one field guide to the competition.

Rocks

There are three classifications of rocks: igneous, metamorphic, and sedimentary. Any type of rock can be transformed into the other 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 rocks occur 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.
Igneous Rocks
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.
Sedimentary Rocks
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 * 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 which have been subjected to heat and pressure. Often these rocks bear little resemblance to their parent rocks.

Metamorphic Rocks
Name Parent Description Grain Color and Foliation Metamorphism
Gneiss Can be formed of 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.

Minerals

By definition, minerals must have a definite chemical and crystal structure. There are a huge 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. I won't attempt to go over all of that here, just look it up 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 and Tectosilicates contain the element silicon.

Formula
Each mineral has a definite chemical composition. For example, copper difluorite is CuF_2?. Again, if you need a review on chemical formulas, look in any chemistry textbook.
Color
Color is not a reliable way to identify a mineral! Some minerals can be any color under the sun. While color can sometimes be useful, don't rely on it!
Streak
Streak is the color you get when you rub a rock across an unglazed piece of porcelain. Streak is much more useful than color because a mineral always has the same streak.
Luster
A mineral's luster is the way it reflects light. Descriptions of luster are very subjective, but 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 the mineral grows in. A good mineral book, like the Peterson Field Guide, will tell about 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, you can use common objects to see if the 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, you can tell whether a mineral specimen is "light" (usually less that 3.5) or "heavy" (greater than 4). Specific gravity can be helpful in detecting metallic minerals (they are usually heavier), or in 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. It 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 will not list the characteristics of every mineral; however, you can get all that information from any good mineral identification handbook. You could go and learn every characteristic of every mineral, but it is a good idea to only try and memorize the one distinguishing characteristic of each mineral so that you can easily identify it without having to memorize too much. A short description that helps you remember that mineral is also a good idea to remember.

Mineral Name Description

Name Hardness SG Streak Color Group Crystal Shape
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 Hydroxides 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


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
Augite is 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 we usually see in Science Olympiad are mostly light green and opaque. Often have hexagonal crystal. Aquamarine and Emerald
Biotite
Black mica--it's thin and platy. It comes off in thin sheets.
Bornite
"Peacock Copper." It has a dark, purplish-blue 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's a little softer and it has a more rhombus like shape. It also bubbles in hydrochloric acid (HCl), but most people don't 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
looks like, well, copper. You can usually 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
You can often see 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 salmony-pink color. It has a very distinctive luster.
Flourite
Almost any color. Hard to distinguish from calcite, but it's a little harder. Usually has dipyramidal or cubic structure.
Galena
It has perfect cubic cleavage and is very heavy. It is made of lead sulfide and is a important lead ore.
Goethite
Another "black rock". This one sometimes has a slightly iridescent tarnish, though. It has been described as an "ugly brownish orange-black rock"
Gold
Gold is...well gold colored. Don't confuse with pyrite. Typically smoother than pyrite. Also, gold generally forms nuggets, while pyrite usually forms cubic crystals.
Graphite
Silver, shiny, soft, and leaves dark smudges on your hands. Used for pencil lead.
Gypsum
Looks like any number of transparent colorless minerals, but luckily gypsum is very soft and easily scratched with your 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 you can usually identify 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's 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. It is usually white and orange.
Lepidolite
A very pretty pink or lilac color. It 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's magnetic. If you don't have the equipment to check for that, it 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. It is 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. It's 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. It has a resinous luster.
Staurolite
Almost always forms short, prismatic crystals. It's usually brown, and sometimes forms cruciform twins.
Sulfur
It's 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's surface. Pleochroric (same crystal appears different color depending on viewing angle).
Tremolite
Usually comes in small, bladed crystals. It's light-colored and sometimes transparent. Commercially, tremolite was used as asbestos.
Ulexite
Almost always white, and looks like a densely-packed bundle of white threads. It's opaque in one direction, and conducts light in the other. It's 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 analyzed his results. The reaction series helps to explain why certain minerals are commonly found together, while others are rare combinations.

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 does.

This 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.

Bowen.gif

Picking a Field Guide

It is probably a good thing to use a binder over a field guide, since not only can you organize it at your own discretion, you can learn the facts and pseudo-memorize them as you create your sheets (plus it's great for general geology/petrology/mineralogy notes). However, if you like to use field guides, here is a guide to picking one by a SO veteran:

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's quite concise and efficient - very reliable. Not the easiest read, but definitely numero uno. Hands down.

Peterson: Ehh, a not-so-close second, but a clear silver medalist here. Not as informative as S&S, but does have nice pictures and good ID tips. I like the layout. Good backup.

Audubon: Personally, I think this guide is pretty good, but not the best.- 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 ID 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? (Protip: it's perfectly okay to splice pages of your field guide into your binder).

Advice

  1. Speed is the key; Rocks & Minerals is a very fast-paced event, and you need to be able to find what you want quickly because most stations have multiple tasks in a short time period, so organization is very important. Make sure you can quickly find information in your book and binder. If you minimize the amount of information you bring, the amount of information you have to sort through to get to what you want will be less. As a rule of thumb, keep it travel size: a one-inch binder should be plenty, and a fairly good book will do.
  2. If you want to be successful, don't just read this and expect it to tell you everything. Get a couple of good books and get to know them really, really well. Eventually you won't need the books for basic identification, but it's always good to keep them around just in case.
  3. 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) and the Eyewitness Handbook.
  4. If you're really serious, buy or borrow a college book on geology or mineralogy. There are also a lot of good internet resources. I'd suggest starting at http://www.minerals.net. It has good descriptions of minerals, and a lot of nice links.

Links

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