Rocks and Minerals
|Rocks and Minerals|
|Question Marathon Threads|
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.
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.
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.
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.
|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 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.
|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 are composed of other rocks which have been subjected to heat and pressure. Often these rocks bear little resemblance to their parent 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.|
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.
- 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.
- Each mineral has a definite chemical composition. For example, copper difluorite is ?. Again, if you need a review on chemical formulas, look in any chemistry textbook.
- 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 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.
- 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.
- Three axes of symmetry, all at right angles to one another, and all of equal lengths. Sometimes called cubic.
- 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.
- Trigonal is sometimes considered to be separate from hexagonal.
- Three axes, all at right angles to one another, of three different lengths.
- Three unequal axes, two at right angles, and the other inclined.
- Three unequal axes, none of which are at right angles to any others.
- 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 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).
- 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
|Talc||1||2.58-2.83||White||Light to gray, green||Silicates||Monoclinic|
|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|
|Calcite||3||2.71||White grayish||Light medium||Carbonates||Trigonal/ Hex|
|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|
|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|
|Amazonite||6-6.5||2.55-2.63||White||Medium esp. green||Silicates||Triclinic|
|Albite||6-6.5||2.6-2.63||White||Many Esp. Light||Silicates||Triclinic|
|Epidote||6-7||3.35-3.5||Colorless-grayish||Dark or yellowish||Silicates||Monoclinic|
|Almandine (garnet)||6.5-7.5||4.1-4.3||White||Dark esp. brown||Silicates||Cubic|
|Tourmaline Group||7-7.5||3-3.2||Colorless||Medium||Silicates||Trigonal/ Hex|
- White, tan, or cream feldspar
- Dark red, garnet.
- Bright green feldspar.
- Usually green or purple, but can be almost any color.
- white, powdery variety of calcite. Can often form amber colored hexagonal crystals.
- 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.
- Always blue (one of those minerals where color can be depended on), with a blue streak.
- Tan rock with orange, white, and prown pisoliths of aluminum, causing light weight. Formed from weathering of feldspars.
- White and kind of platy, but very heavy because it contains barium. Can form rosettes.
- The cheap specimens we usually see in Science Olympiad are mostly light green and opaque. Often have hexagonal crystal. Aquamarine and Emerald
- Black mica--it's thin and platy. It comes off in thin sheets.
- "Peacock Copper." It has a dark, purplish-blue tarnish. Chalcopyrite, which looks almost the same, tarnishes purple, orange, yellow, and red.
- 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.
- Usually a soft, translucent white or blue.
- Very brassy yellow, tarnishes bright red, purple, yellow, and orange.
- looks like, well, copper. You can usually see the green tarnish.
- very hard reddish or purplish rock. Very hard and often has small column-like opaque crystals. Rubies and Sapphires.
- Adamantine luster. Comes in various lighter colors. Hardest mineral.
- You can often see thin, platy cream-colored crystals. Sometimes there are dark specks embedded between the crystals.
- Mostly greenish-yellow and grainy, but can be almost any shade of green. Often confused with olivine. Described as "pistachio"
- Kind of a salmony-pink color. It has a very distinctive luster.
- Almost any color. Hard to distinguish from calcite, but it's a little harder. Usually has dipyramidal or cubic structure.
- It has perfect cubic cleavage and is very heavy. It is made of lead sulfide and is a important lead ore.
- Another "black rock". This one sometimes has a slightly iridescent tarnish, though. It has been described as an "ugly brownish orange-black rock"
- 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.
- Silver, shiny, soft, and leaves dark smudges on your hands. Used for pencil lead.
- 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.
- 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 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).
- Black with short stubby crystals, and usually striated lengthwise.
- Looks like chalk, but is actually clay. It is usually white and orange.
- 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.
- 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.
- This mineral is easy because it is always green, with a green streak. It is often found with azurite.
- White, yellow, or tan mica--thin and platy.
- Usually light green or yellowish-green. Transparent specimens are called peridot.
- Precious opal is iridescent, but most opal is white and opaque with a greasy or waxy luster. Usually amorphous crystals.
- 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.
- 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.
- Comes in all shades of pink and red. It's usually massive, but sometimes crystalline.
- 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.
- Always blue, but usually a very dark, mottled blue. Its darker color and colorless streak tell it apart from azurite.
- 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.
- Almost always forms short, prismatic crystals. It's usually brown, and sometimes forms cruciform twins.
- It's always some shade of yellow, and it gives off a sulfurous odor when rubbed.
- Very soft, often light green, white, or grey and feels very waxy.
- Extremely variable color, but usually comes in well-formed prismatic crystals. A light colored gem
- 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).
- Usually comes in small, bladed crystals. It's light-colored and sometimes transparent. Commercially, tremolite was used as asbestos.
- 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.
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 to much and unimportant. The pictures are usually good, and 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).
- 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.
- 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.
- 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.
- 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.