Identify Common Minerals

Collecting minerals can be a fun hobby, partly because there are so many types to identify. There are many tests you can conduct without specialized equipment to narrow down the possibilities, and a handy description of common minerals on this page to compare with your result. You can even skip straight down to those descriptions to see if a specific question you have is easily answered without testing. For instance, it will teach you how to tell real gold from other shiny, yellow minerals; learn about striped, shiny, colorful bands you find in rocks; or identify a strange mineral that peels into sheets when you rub it.

Steps

Conducting Tests

  1. Tell minerals and rocks apart. A mineral is a naturally occurring combination of chemical elements in a certain structure. While a single mineral can appear in different shapes or colors due to geological processes or trace amounts of impurities, generally every example of that mineral will have certain characteristics that can be tested for. Rocks, on the other hand, may be formed from a combination of minerals and don't have a crystal structure. They aren't always easy to tell apart, but if these tests produce different results on one part of an object than on another, the object is probably a rock.
    • You can try Identify-Igneous-Rocks as well, or at least identifying which of the three types of rock they belong to.
  2. Understand mineral identification. There are thousands of minerals on Earth, but many of them are rare or only found deep underground. Sometimes, conducting two or three tests is all you need to narrow the unidentified substance down to a likely, common mineral listed in the next section. If your mineral's characteristics don't match any of those descriptions, try to find a mineral identification guide for your area. If you've conducted many tests and can't narrow a mineral down between two or more possibilities, search online for photographs of each possible mineral and for specific tips for telling those minerals apart.
    • It's best to include at least one test that involves an action, such as the hardness test or streak test. Tests that only involve looking at and describing the mineral may not be helpful by themselves, since different people describe the same mineral in different ways.
  3. Examine the shape and surface features of the mineral. The overall shape of each mineral crystal and the pattern of a group of crystals is called a habit.[1] There are many technical terms geologists use to describe this, but a basic description is often enough. For instance, is the mineral bumpy or smooth? Is it a collection of rectangular crystals jumbled into each other, or thin spiky crystals pointed outward?
  4. Look at your mineral's shine, or luster. Luster is the way a mineral reflects light, and while it's not a scientific test, it's often useful to include in descriptions. Most minerals have a shine that's either glassy (or vitreous) or metallic. You can also describe a shine as greasy, pearly (a whitish shine), earthy (dull, like unglazed pottery), or with any description that makes sense to you.[2] Use multiple adjectives if you need to.
  5. Take a look at the mineral's color. For most people, this is one of the easiest tests to conduct, but it's not always useful. Small traces of other substances in the mineral can cause it to change color, so one mineral may appear in many different colors. However, if the mineral is an unusual color, such as purple, it might help you narrow down the possibilities.
    • When describing minerals, avoid hard-to-define color words such as "salmon" and "puce." Stick with simple terms such as "red," "black," and "green."
  6. Conduct a streak test. This is a useful and easy test, as long as you have a piece of white, unglazed porcelain. The back of a kitchen of bathroom tile might work well; see if you can purchase one at a home improvement store. Once you have the porcelain, simply rub the mineral on the tile, and see what color "streak" it leaves behind. Often, this streak is a different color than the large piece of mineral.
    • Glaze is what gives porcelain and other ceramic objects their glassy shine. An unglazed piece of porcelain does not reflect light.
    • Keep in mind that some minerals have no streak, particularly the harder minerals (because they are harder than the streak plate).
  7. Test the material's hardness. Geologists often use the Mohs hardness scale, names after its creator, to quickly estimate the hardness of a mineral. If you succeed with the "4" test but not with the "5," the mineral's hardness is between 4 and 5, and you can stop testing. Try to leave a permanent scratch mark using these common materials (or minerals found in mineral hardness test kit), starting with the lowest numbers and working upward if the test succeeds:[3]
    • 1 -- Easily scratched with fingernail, feels greasy and soft (or can be scratched with talc)
    • 2 -- Can be scratched by a fingernail (gypsum)
    • 3 -- Can be cut easily with a knife or a nail, scratched by a penny (calcite)
    • 4 -- Can be scratched easily by a knife (fluorite)
    • 5 -- Can be scratched by a knife with difficulty, scratched by a piece of glass (apatite)
    • 6 -- Can be scratched by a steel file, scratches a piece of glass with difficulty (orthoclase)
    • 7 -- Scratches a steel file, easily scratches a piece of glass (quartz)
    • 8 -- Scratches quartz (topaz)
    • 9 -- Scratches almost anything, cuts glass (corundum)
    • 10 -- Scratches or cuts almost anything (diamond)
  8. Break the mineral and see how it comes apart. Since each specific mineral has a certain structure to it, it should break in a certain way. If the break results in one ore more flat surfaces, it demonstrates cleavage. If there are no flat surfaces, just curves or irregular bumps, the broken mineral has fracture.[4]
    • Cleavage can be described in more detail by the number of flat surfaces that a break creates (usually between one and four), and whether the surface is perfect (smooth) or imperfect (rough).
    • Fracture comes in several types. Describe it as splintered (or fibrous), sharp and jagged (hackly), bowl-shaped (conchoidal), or none of the above (uneven).
  9. Conduct other tests if the mineral is still unidentified. There are many other tests geologists conduct to identify a mineral. However, many of these are almost never useful for common minerals, or they may involve specialized equipment or dangerous materials. Here are brief descriptions of some tests you might be interested in conducting:
    • If your mineral sticks to a magnet, it is most likely magnetite, the only common strongly magnetic mineral. If the attraction is weak, or descriptions of magnetite don't match your mineral, it may be pyrrhotite, franklinite, or ilmenite instead.[5]
    • Some minerals melt easily in a candle or lighter flame, while others won't melt even in a blowtorch flame. Minerals that melt easily have a higher "fusibility" than minerals that are more difficult to melt.
    • If your mineral has a notable smell, try to describe it and search online for a mineral with that smell. Strong smelling minerals are not common, although the bright yellow mineral sulfur can react to produce the smell found in rotten eggs.

Identifying Common Minerals

  1. Refer to the previous section if you don't understand a description. The descriptions below use various terms or numbers to describe the mineral's shape, hardness, appearance after breaking, or other attributes. If you're not sure what these mean, refer to the section above on conducting tests for an explanation.
  2. Crystalline minerals are most often quartz. Quartz is an extremely common mineral, and its glittering or crystalline appearance catches the eye of many collectors. Quartz has a hardness of 7 on the Mohs scale, and demonstrates any type of fracture when broken, never the flat surface of cleavage.[6] It does not leave a noticeable streak on white porcelain. It has a glassy luster, or shine.
    • Milky quartz is translucent, rose quartz is pink, and amethyst is purple.
  3. Hard, glassy minerals without crystals may be a different type of quartz, called chert. All types of quartz are crystalline, but some varieties, called "cryptocrystalline," are made of minuscule crystals not visible to the eye.[6][7] If the mineral has a hardness of 7, fractures, and has a glassy luster, it may be a type of quartz called chert. This is most commonly brown or grey.
    • "Flint" is one variety of chert, but it is categorized in many different ways. For instance, some people may refer to any black chert as flint, while others may only call it flint if it has a certain luster or was found among certain types of rock.
  4. Minerals with striped bands are usually a type of chalcedony. Chalcedony is formed from a mixtures of quartz and another mineral, moganite. There are many beautiful varieties, typically forming striped bands of different colors. Here are two of the most common:
    • Onyx is a type of chalcedony that tends to have parallel bands. It is most often black or white, but can be many colors.
    • Agate has more curving or "wiggly" bands, and can show up in a wide variety of different colors. It can form from pure quartz, chalcedony, or similar minerals.
  5. See if your mineral's characteristics match feldspar's. Besides the many varieties of quartz, feldspar is the most common type of mineral found. It has a hardness of 6, leaves a white streak, and can appear with various colors or luster. It forms two flat cleavages when broken, with surfaces that are fairly smooth and nearly at right angles to each other.
  6. If the mineral peels when rubbed, it is probably mica. This mineral is easily identified because it peels into thin, flexible sheets when scratched by a fingernail or even rubbed with a finger. Muscovite mica or white mica is pale brown or colorless, while biotite mica or black mica is dark brown or black, with a brown-gray streak.[7][6]
  7. Learn the different between gold and fool's gold. Pyrite, also known as fool's gold, has a metallic yellow appearance, but several test can distinguish it from real gold. It has a hardness rating of 6 or more, while gold is much softer, with a rating between 2 and 3.[8] It leaves a greenish-black streak, and can be crushed into powder if enough pressure is applied.
    • Marcasite is another common mineral similar to pyrite. While pyrite crystals are shaped like cubes, marcasite forms needles.
  8. Green and blue minerals are often malachite or azurite. Both of these minerals contain copper, among other minerals. The copper gives malachite its rich green color, while it causes azurite to appear bright blue. These often occur together, and both have a hardness between 3 and 4.[6]
  9. Use a mineral guide or website to identify other types. A mineral guide specific to your area will cover other common types of mineral found in that region. If you are having difficulty identifying a mineral, some online resources such as minerals.net will let you search for the results of your tests and match them to possible minerals.

Tips

  • To keep yourself organized, make a list of all minerals that share the characteristics you've discovered so far. Every time you discover something new about your mineral, cross off the minerals that yours could not be. Hopefully, you will end up with only one left - your mineral.

Warnings

  • Hydrochloric acid tests, not described here, are useful in a small number of common cases. Acid can cause serious damage to skin and eyes, so only perform this test with safety equipment and adult supervision.

Things You'll Need

  • Unglazed porcelain tile (called a streak plate)
  • Magnet (optional)

to test for hardness:

  • penny
  • steel file
  • iron nail
  • Mineral identification booklet or website (if your mineral is not described on this page)

Related Articles

Sources and Citations

  1. ↑ http://www.minsocam.org/msa/collectors_corner/id/mineral_id_keyi8.htm
  2. ↑ http://flexiblelearning.auckland.ac.nz/rocks_minerals/minerals/lustre.html
  3. ↑ http://www.britannica.com/EBchecked/topic/387714/Mohs-hardness
  4. ↑ https://www.wikihow.com/index.php?title=Identify-Common-Minerals&action=submit
  5. ↑ http://www.minsocam.org/msa/collectors_corner/id/mineral_id_keyi1.htm
  6. ↑ 6.0 6.1 6.2 6.3 http://skywalker.cochise.edu/wellerr/GLG101/GLG101-20-minerals.htm
  7. ↑ 7.0 7.1 http://www.pitt.edu/~cejones/GeoImages/1Minerals.html
  8. ↑ http://www.esci.umn.edu/courses/1001/minerals/pyrite.shtml
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