10 Steps for Easy Mineral Identification

Young girl studying a collection of gems and minerals using a magnifying glass and brush to collect information while sitting at a desk. Childhood. Science. — Cyndi Monaghan/Getty Images

Science

Geology

Have pen and paper or a computer handy to record your notes.

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Pick Your Mineral

Use the largest mineral sample you can find. If your mineral is in pieces, bear in mind that they may not all be from the same rock. Finally, make sure your sample is free of dirt and debris, clean and dry. Now you're ready to begin identifying your mineral.

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Luster

Luster describes the way a mineral reflects light. Measuring it is the first step in mineral identification. Always check for luster on a fresh surface; you may need to chip off a small portion to expose a clean sample. Luster ranges from metallic (highly reflective and opaque) to dull (nonreflective and opaque). In between are a half-dozen other categories of luster that assess the degree of a mineral's transparency and reflectivity.

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Hardness

Hardness is measured on the 10-point Mohs scale, which is essentially a scratch test. Take an unknown mineral and scratch it with an object of known hardness (like a fingernail or a mineral like quartz). Through trial and observation, you can determine your mineral's hardness, a key identification factor. For example, powdery talc has a Mohs hardness of 1; you could crumble it between your fingers. A diamond, on the other hand, has a hardness of 10. It's generally considered to be the hardest material known to human.

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Color

Be observant but cautious — Beware of color until you've learned what colors to trust. Andrew Alden

Color is important in mineral identification. You'll need a fresh mineral surface and a source of strong, clear light to examine it in. If you have an ultraviolet light, check to see if the mineral has a fluorescent color. Make note if it displays any other special optical effects, such as iridescence or changes in color.

Color is a fairly reliable indicator in the opaque and metallic minerals like the blue of the opaque mineral lazurite or the brass-yellow of the metallic mineral pyrite. In translucent or transparent minerals, however, color is less reliable as an identifier because it is usually the result of a chemical impurity. Pure quartz is clear or white, but quartz can have many other colors.

Try to be precise in your identification. Is it a pale or deep shade? Does it resemble the color of another common object, like bricks or blueberries? Is it even or mottled? Is there one pure color or a range of shades?

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Streak

True colors — Streak is an easy test that's sometimes definitive. Andrew Alden

Streak describes the color of a finely crushed mineral. Most minerals leave a white streak, regardless of their overall color. But a few minerals leave a distinctive streak that can be used to identify them. To identify your mineral, you'll need a streak plate or something like it. A broken kitchen tile or even a handy sidewalk can do.

Scratch your mineral across the streak plate with a scribbling motion, then look at the results. Hematite, for example, will leave a red-brown streak. Bear in mind that most professional streak plates have a Mohs hardness of about 7. Minerals that are harder than that will scratch the place and won't leave a streak.

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Mineral Habit

Typical shapes that minerals like — Crystal form requires study; mineral habit, not so much. Andrew Alden

A mineral's habit (its general form) can be especially useful for identifying some minerals. There are more than 20 different terms describing habit. A mineral with visible layers, like Rhodochrosite, has a banded habit. Amethyst has a drusy habit, where jagged projectiles line a rock's interior. Close observation and perhaps a magnifying glass are all you need for this step in the mineral identification process.

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Cleavage and Fracture

Watch the pieces — How minerals break is a key clue to their identification. Andrew Alden

Cleavage describes the way a mineral breaks. Many minerals break along flat planes or cleavages. Some cleave in only one direction (like mica), others in two directions (like feldspar), and some in three directions (like calcite) or more (like fluorite). Some minerals, like quartz, have no cleavage.

Cleavage is a profound property that results from a mineral's molecular structure, and cleavage is present even when the mineral doesn't form good crystals. Cleavage can also be described as perfect, good or poor.

Fracture is breakage that is not flat and there are two types: conchoidal (shell-shaped, as in quartz) and uneven. Metallic minerals may have a hackly (jagged) fracture. A mineral may have good cleavage in one or two directions but fracture in another direction.

To determine cleavage and fracture, you'll need a rock hammer and a safe place to use it on minerals. A magnifier is also handy, but not required. Carefully break the mineral and observe the shapes and angles of the pieces. It may break in sheets (one cleavage), splinters or prisms (two cleavages), cubes or rhombs (three cleavages) or something else.

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Magnetism

A mineral's magnetism can be another identifying characteristic in some instances. Magnetite, for example, has a strong pull that will attract even weak magnets. But other minerals have only a weak attraction, notably chromite (a black oxide) and pyrrhotite (a bronze sulfide). You'll want to use a strong magnet. Another way to test magnetism is to see if your specimen attracts a compass needle.

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Other Mineral Properties

Sometimes these tests pay off — A few other tests may sometimes be exactly the right one for certain minerals. Andrew Alden

Taste can be used to identify evaporite minerals (minerals formed by evaporation) like halite or rock salt because they have distinctive tastes. Borax, for instance, tastes sweet and slightly alkaline. Be careful, though. Some minerals can sicken you if ingested in sufficient quantities. Gently touch the tip of your tongue to a fresh face of the mineral, then spit it out.

Fizz means the effervescent reaction of certain carbonate minerals the presence of an acid like vinegar. Dolomite, found in marble, will fizz actively if dropped in a small bath of acid, for example.

Heft describes how heavy or dense a mineral feels in the hand. Most minerals are about three times as dense as water; that is, they have a specific gravity of about 3. Make note of a mineral that is noticeably light or heavy for its size. Sulfides like Galena, which is seven times more dense than water, will have a notable heft.

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Look It Up

The final step in mineral identification is to take your list of characteristics and consult an expert source. A good guide to rock-forming minerals should list the most common, including hornblende and feldspar, or identify them by a common characteristic like metallic luster. If you still can't identify your mineral, you may need to consult a more comprehensive mineral identification guide.