Collecting minerals can be a fun hobby, not least because there are so many to identify. There are a variety of tests you can conduct - without specific equipment - to narrow down the possibilities, and the brief description of the minerals in this article can help you check your results. You can also skip straight to the descriptions to see if a specific question finds a simple answer without testing. For example, this article will teach you to distinguish gold from other bright and yellow minerals; discover the differences between the bright and colorful stripes you see on the rocks; or identify a strange mineral that flakes off when you rub it.
Steps
Part 1 of 2: Conducting Tests
Step 1. Make a distinction between minerals and rocks
A mineral is a naturally variable combination of chemical elements in a given structure. A simple mineral can have different shapes or colors based on geological processes or traces of impurities, but generally each specimen has specific characteristics that can be tested. Rocks, on the other hand, can be formed through the combination of minerals and do not have a crystalline structure. It's not always easy to tell them apart, but if these tests produce different results on two distinct objects, one of them is definitely a rock.
You can also identify a rock, or at least understand which of the three types it belongs to
Step 2. Learn to identify the minerals
There are thousands of minerals on Earth, but many are rare and found only deep in the ground. Sometimes, it is enough to conduct a couple of tests to understand that the unknown substance is a common mineral, the list of which can be found in the next section. If the characteristics of your mineral do not match the descriptions, look for a guide in your area. If you've run a lot of tests but can't rule out two or more possibilities, search online photos of every possible mineral for specific advice on how to tell them apart.
It would be best to always include a test that involves an action, such as the hardness test or the color test. Tests involving mere observation and description of the mineral may be ends in themselves, as different people describe the same mineral differently
Step 3. Examine the shape and surface of the mineral
The shape of each crystalline mineral and the structure of a group of crystals is called crystalline dress. There are many technical terms that geologists use to describe it, but the basic description is usually sufficient. For example, is the mineral smooth or rough? Is it made up of a series of rectangular crystals set together, or are they thin, pointed and facing inwards?
Step 4. Observe the brilliance of your mineral, or sheen
Luster is how crystal reflects light, and while it's not a scientific test, it's often useful enough to be included in descriptions. Many minerals have both a glassy and metallic luster. You can also describe sheen as oily, pearly (a whitish sheen), resinous (dull, like unpolished ceramic), or with any description that makes sense to you. Use more adjectives if necessary.
Step 5. Observe the color of the mineral
For most people this is the easiest test to conduct, but it doesn't always come in handy. Small traces of other substances in the mineral can change its color, so the same can have different shades. However, if the mineral has an unusual color, such as purple, it may help you prune the possibilities.
When describing minerals, avoid hard-to-define terms like salmon and flea. Use simpler ones, like red, black, and green
Step 6. Conduct a smear test
It's a simple and useful test, and all you need is a piece of unglazed porcelain. The back of a kitchen or bathroom tile will do just fine; buy one at a construction store. When you have porcelain, just rub the mineral on the tile and see what a smear it leaves. Often, the smear is a different color than the piece of mineral.
- Glaze is what gives porcelain or other ceramic objects the shiny appearance. An unglazed piece of porcelain does not reflect light.
- Remember that some minerals do not leave a trace, especially those that are particularly hard (as they are harder than the material used as a dish).
Step 7. Test the hardness of the material
Geologists often use the Mohs scale, named in honor of its creator, to quickly estimate the hardness of a mineral. If you are successful with test 4 but not with 5 the hardness of the mineral is between 4 and 5, and you can stop the tests. Try to leave a permanent scratch using these common materials (or those you can find in the hardness measurement kit), starting with the lowest numbers and going up until the test passes:
- 1 - They are scratched with the nail, they are fat and tender (or they are scratched with talc)
- 2 - They are scratched with the nail (plaster)
- 3 - They are cut with a knife or a file, they are scratched with a coin (calcite)
- 4 - They are scratched with a knife (fluorite)
- 5 - They are scratched with difficulty with a knife, easily with a piece of glass (apatite)
- 6 - They can be scratched with a steel point, they scratch a piece of glass with difficulty (orthoclase)
- 7 - They scratch a steel point, they scratch a piece of glass (quartz)
- 8 - Rigano quartz (topaz)
- 9 - They strip almost everything, cut the glass (corundum)
- 10 - They line or cut almost everything (diamond)
Step 8. Break the ore and see how it splits
Since every single mineral has a certain structure, it should break down in a specific way. If it breaks into one or more flat surfaces, it shows that it has properties of cleavage. If there are no flat surfaces, but only curves and irregular pieces, the broken ore has one fracture.
- Cleavage can be described in more detail by the number of flat surfaces created by the break (usually between one and four), and whether they are perfect (smooth) or imperfect (rough).
- There are several types of fractures. It can be chipped (or fibrous) if the surface is covered with splinters or fibers, scaly if it is irregular, sharp, conchoid whether it has a smooth, curved surface or none of these (irregular).
Step 9. Conduct further tests if you have not yet identified the mineral
There are many other tests that geologists conduct to recognize a mineral. However, many of these are usually not useful for common minerals, or they may require specific equipment or hazardous materials. Here are brief descriptions of some tests you may be conducting:
- If your mineral is attracted to a magnet, it is probably magnetite, the only strongly magnetic mineral. If the attraction is weak, or the description of the magnetite does not match your mineral, it could be pyrrhotine, franklinite or ilmenite.
- Some minerals dissolve easily when approached to a candle or lighter, while others would not change state even in flames. Minerals that dissolve easily have a higher melt than others.
- If your mineral has a particular smell, try to describe it and search online for minerals with that smell. Strong-smelling minerals are not common, although a bright yellow sulfur mineral can react and produce a smell similar to that of rotten eggs.
Part 2 of 2: Recognizing Common Minerals
Step 1. Refer to the previous section if a description is not clear to you
Those that will be made below use various terms to describe the shape, hardness and appearance of a mineral after breaking, or other characteristics. If you're not sure you understand what they mean, refer to the previous section or conduct tests to clarify your ideas.
Step 2. Crystalline minerals are usually quartz
Quartz is a very common mineral, and its bright or crystalline appearance attracts the attention of many collectors. Quartz has a hardness of 7 on the Mohs scale, and demonstrates all sorts of fractures once broken, and never the flat surface of a cleavage. It does not leave a visible smear on white porcelain. It has a glassy luster.
The milky quartz is translucent, the rose quartz is pink and the amethyst it is purple.
Step 3. The hard, shiny minerals without crystals might be a different type of quartz, called flint
All quartzes are crystalline, but some varieties, called cryptocrystallines, are made of tiny crystals not visible to the human eye. If the mineral has a hardness of 7, fractures, and a glassy sheen, it could be one flint. It is usually brown or gray.
"Silica" is a variety of flint, but it is categorized in many different ways.. For example, some might call every black flint a silica, while others might call silica only a mineral with a certain sheen or found only among particular types of rocks
Step 4. Striped minerals are usually a type of chalcedony
Chalcedony is made up of a mix of quartz and another mineral, morganite. There are several beautiful varieties of this mineral, usually with stripes of different colors. Here are the two most common:
- Onyx is a type of chalcedony that tends to have parallel stripes. It is usually black or white, but it can be of many colors.
- Agate has more curved or meandering stripes, and can be found in a wide variety of colors. It can be formed from pure quartz, chalcedony or similar minerals.
Step 5. Check if your mineral has the characteristics of feldspar
In addition to the many varieties of quartz, the feldspar it is one of the most common minerals. It has a hardness of 6, leaves a white smear and can be of different colors and luster. It forms two flat cleavages when broken, with rather smooth surfaces close to the right ends of the mineral.
Step 6. If the mineral flakes when rubbed, it is probably mica
It can be easily recognized because it flakes into thin sheets when rubbed with a fingernail or even a finger. There not muscovite or white mica is a pale brown or colorless, while the mica biotite or black mica is dark brown or black, with a brown-gray smear.
Step 7. Learn to distinguish gold from fool's gold
There pyrite, also called "fool's gold", has a metallic yellow appearance, but there are various tests that can distinguish it from gold. It has a hardness of 6 or higher, while gold is much softer, with an index between 2 and 3. It leaves a greenish-black streak, and can be pulverized if enough pressure is applied.
There marcasite is another common mineral similar to pyrite. While the pyrite crystals have a cubic signature, marcasite forms needles.
Step 8. Blue and green minerals are often malachite or azurite
Both contain copper, among other minerals. Copper gives to malachite its intense green color, while making the azurite bright blue. They are usually found in the same reservoir, and have a hardness between 3 and 4.
Step 9. Use a mineral guide or website to identify other types
A guide to minerals specific to your area may cover all the types you might find in your region. If you're having a hard time recognizing a mineral, there are online resources that can come in handy.
