How to Identify Minerals in 10 Steps
How to Identify Minerals in 10 Steps
Step 1: Pick Your Mineral
Learning mineral identification is like learning to cook. You begin by following step-by-step procedures and looking up a lot of things. But after a while you notice regularities, become familiar with the usual suspects, make some productive mistakes, and get better at it until it becomes easy and fun.
Another way mineral identification is like cooking is that professionals can go to school, learn to use expensive equipment and master the subject fully, yet amateurs can handle nearly all the common possibilities using just a few simple tools.The first thing to do is to observe and test your mineral.Use the largest piece you can find, and if you have several pieces, make sure sure that they are all the same mineral. Examine your mineral for all of the following properties, writing down the answers. After that you’ll be ready to take your information to the right place.
Step 2: Luster
Luster is the way a mineral reflects light and the first key step in mineral identification. Look for luster on a fresh surface. The three major types of luster are metallic, glassy (vitreous) and dull. A luster between metallic and glassy is called adamantine, and a Luster between glassy and dull is called resinous or waxy.
Step 3: Hardness
Use the 10-point Mohs hardness scale. The important hardnesses are between 2 and 7. For this you’ll need your fingernail (hardness about 2), a coin (hardness 3), a knife or nail (hardness 5.5) and a few key minerals.read about Hardness
Step 4: Color
Color is important in mineral identification, but it can be a complicated subject. Experts use color all the time because they have learned the usual colors and the usual exceptions for common minerals. If you’re a beginner, pay close attention to color but do not rely on it. First of all, be sure you aren’t looking at a weathered or tarnished surface, and examine your specimen in good light.
Color is a fairly reliable indicator in the opaque and metallic minerals—for instance the blue of the opaque mineral lazurite or the brass-yellow of the metallic mineral pyrite. In the translucent or transparent minerals, color is usually the result of a chemical impurity and should not be the only thing you use. For instance, pure quartz is clear or white, but quartz can have many other colors.
Try to be precise with color. 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?
If you have an ultraviolet light, this is the time to see if the mineral has a fluorescent color. Make note if it displays any other special optical effects.
Step 5: Streak
Streak is the color of the finely crushed mineral. Streak is somewhat more reliable than color and is essential for a few minerals. 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.
Step 6: Crystal Form and Mineral Habit
A good knowledge of crystals is very helpful once you’re past the beginner stage, but often minerals do not display any crystal faces, so for simplicity’s sake we’ll ignore it. For beginners, a mineral’s crystal form is less important than its cleavage (see the next step). When you’re ready to learn this aspect of minerals, you’ll want a book.
One thing even beginners can do, though, is to observe a mineral’s habit, the general form it takes.
One thing even beginners can do, though, is to observe a mineral’s habit, the general form it takes.
Step 7: Cleavage and Fracture
Cleavage is the way a mineral breaks. Many minerals break along flat planes, or cleavages—some 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. The two main kinds of fracture are 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.
Step 8: Magnetism
Magnetism is a distinctive property in a few minerals. Magnetite is the prime example, but a few other minerals may be weakly attracted by a magnet, notably chromite (a black oxide) and pyrrhotite (a bronze sulfide). Use a strong magnet. The magnets I use came from the corners of an old plastic shower curtain. Another way to test magnetism is to see if the specimen attracts a compass needle.
Step 9: Other Mineral Properties
Taste is definitive for halite ( rock salt ), of course, but a few other evaporite minerals also have distinctive tastes. Just touch your tongue to a fresh face of the mineral and be ready to spit—after all it’s called taste, not flavor. Don’t worry about taste if you don’t live in an area with these minerals.
Fizz means the effervescent reaction of certain carbonate minerals to the acid test. For this test, vinegar will do.
Heft is how heavy a mineral feels in the hand, an informal sense of density. 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. Galena, on the right, is distinctly heavy. Sulfides and oxides tend to be dense.
Step 10: Look It Up
Now you are ready for mineral identification. Once you have observed and noted these mineral properties, you can take your information to a book or to an online resource. Start with my table of the rock-forming minerals, because these are the most common and the ones you should learn first. Each mineral’s name is linked to a good photograph and notes to help you confirm the identification. If your mineral has metallic luster, go to my Minerals with Metallic Luster gallery to see the most likely minerals in this group. If your mineral is not one of these, try the sources in the Mineral Identification Guides category.
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