Although there are about 3,000 kinds of minerals in nature with a wide variety and different forms, there are only around one hundred common kinds. 

 

Therefore, how can you distinguish one from another if there are several minerals in front of you? You can identify them by color, transparency, luster and crystal morphology, which can be seen only with your naked eyes. Then you can use other simple instruments and equipment to measure hardness, cleavage, luminescence, magnetism and other properties of the mineral powder. 

 

The specific methods are as follows:

 

 

Color recognition is an intuitive way as well as the first step in observation. Many minerals have their own color, such as orange, brown, yellow, green and blue.

 

Red rhodochrosite

 

Pyrite 

 

Blue fluorite 

 

Blue lapis lazuli

 

Green malachite

 

Green calaite

 

Most minerals have multiple colors, and different minerals often have the same color. So it’s not easy to differentiate one from another by color alone. For example, chalcopyrite is similar to gold in color, but its value is far from that of gold. 

 

Golden chalcopyrite grows with red crystal.

 

 

Most minerals are opaque or translucent, and only a few minerals can be completely transparent like glass in the light, such as some kinds of quartz, gypsum and Iceland spar.

 

Yellowish-green transparent quartz 

 

Opaque azurite  

 

Translucent moonstone

 

 

When light shines on minerals, some may pass through, while others will be reflected back. Observing the intensity of the reflected light, the so-called “luster”, is also a way to identify some minerals.

 

Fluorite has glassy luster.

 

Native gold has bright golden luster.

 

Fibrous plaster has silk gloss.

 

Agalmatolite has waxy shine.

 

 

Crystal morphology is one of the most important characteristics to distinguish one kind of mineral from another. Different minerals have different growth habits. Some minerals always grow in one direction and become columnar or finer needle. 

 

Columnar stibnite 

 

Needle-shaped stibnite

 

Others prefer to grow in both directions, becoming platelets or thinner sheets.

 

Mica in the shape of a thin sheet

 

Molybdenite sheet

 

What’s more, some crystals are growing in three directions, forming granular minerals. 

 

Granular lead 

 

Cubic pyrite

 

In fact, there are few individual mineral crystals in nature. The mineral crystals usually appear in the form of mineral cluster. There are even some minerals whose crystal morphology can’t be seen at all, with only a cluster to be seen.

 

Radial mineral cluster of actinolite

 

Kidney-shaped hematite

 

 

Another strange thing about minerals is that the color of many minerals is different from that of their powder. Usually, you can pick up the mineral, scratch it on the white unglazed porcelain plate, and then observe the color left by this scratch, which is called stripe color.

 

The stripe mark of pyrite is black (left).

The streak of transparent rhodochrosite is white (right).

 

 

After long-term research, geologists have found that the hardness and softness of minerals are quite different, but there are still general rules to follow. Minerals containing water molecules such as carbonate, sulfate and phosphate are usually soft, while oxides and silicate minerals without water molecules are relatively hard. 

 

In 1812, to express the hardness of minerals, a German mineralogist first proposed a standard, namely Moh’s hardness, which is expressed by the measured depth of scratches with 1-10 grades.

 

Soapstone 

 

Diamond, king of hardness

 

 

Many minerals will crack in a certain direction when struck by external forces. Generally speaking, this direction is the part with the weakest atomic bond bonding force in the mineral crystal structure, which is the cleavage surface.

 

Iceland spar

 

Native gold with jagged fracture

 

Obsidian with shell-shaped fracture

 

 

Luminosity is the unique physical property of some minerals. When they are irritated by external factors like ultraviolet, X-ray, hit, friction and heat, they can emit visible light.

 

Fluorescence of fluorite 

 

Apatite 

 

 

Magnetic minerals are mainly magnetite and pyrrhotite, which can be attracted by ordinary magnets.

 

Sinan (a compass in ancient China), invented in the Warring States Period, can help people identify directions. It is the application of the physical characteristics of natural magnet ore.

 

Pyrrhotite

 

Magnetite