The physical qualities of most minerals may be used to describe and classify them: hardness, luster, color, streak, specific gravity, cleavage, fracture, and tenacity. These properties can be useful in identifying minerals after they have been found but are also good indicators of the presence of elements that may not be readily visible to the naked eye.
Hardness is the resistance of a mineral to breaking or crushing. The harder a mineral is, the more difficult it will be to break it. Hardness can be measured on a scale from 1 to 10 with 10 being the hardest. Quartz (the main component of glass) has a hardness of 7 while diamond has a hardness of 10. Some minerals are very hard while others are so-called soft stones. For example, soapstone is a hard stone while soap bubbles are quite soft.
Luster is the appearance of brightness or shininess. Many minerals have a bright luster such as quartz or emeralds. Other minerals do not have any luster at all such as gypsum or plaster of Paris.
Color refers to the range of colors that can be expressed by a single element. For example, red ores contain the chemical element iron whereas yellow ores contain the chemical element gold.
The most useful physical features for identifying most minerals are color, luster, streak, hardness, cleavage, fracture, and crystal shape. Other qualities useful in identifying minerals include acid reaction, magnetism, specific gravity, tenacity, taste, odor, feel, and the presence of striations. Some minerals have fluorescent properties when exposed to ultraviolet light.
Minerals are classified according to their physical properties. The three main categories are rock minerals, metal minerals, and fossilized plant and animal materials.
Rock minerals include quartz, limestone, dolomite, gypsum, plaster of Paris, and clay. These are soft substances that can be easily scratched or worn away. They usually have no taste or smell and they may appear white or brownish colored. Rock minerals are generally hard, but some types such as sandstone are not.
Metal minerals include gold, silver, copper, zinc, lead, and iron. These are hard substances that can only be scratched with a special tool called a hammer. They usually have a yellow, white, or red color. Metal minerals also have a tendency to stick to your hammer if you use one on them.
Fossilized plant and animal materials include wood, bone, shell, horn, and ivory. These are hard substances that can only be scratched with great difficulty. They are usually dark colored and have a distinctive odor and taste.
Minerals can be distinguished by their physical properties. Minerals' physical qualities are connected to their chemical makeup and bonding. Some properties, such as a mineral's hardness, are more beneficial for mineral identification than others. For example, hardness differentiates between quartz and flint. Quartz is soft and silky smooth while flint is harder and rougher to the touch. Other properties that may help identify minerals include color, luster, smell, taste, and specific gravity.
Hardness is one of the most useful properties for identifying minerals. The hardness of a mineral is measured on a scale from 1 to 10 with 10 being the hardest. Calcite (calcium carbonate) is very hard (a hardness of 8) while gypsum (calcium sulfate) is very soft (a hardness of 2). Hardness can also be described as brittleness or fractiousness. If you hit a crystal with another piece of glass, it will likely break. This shows that the mineral is hard. On the other hand, if you hit a crystal with another piece of stone, it might score the surface of the stone but would not break. This shows that the mineral is soft and pliable.
Color varies depending on the type of mineral.
The physical features of minerals listed below can be utilized to quickly identify a mineral:
Crystal shape, color, hardness, cleavage, and specific gravity are the most prevalent physical qualities. Examining a mineral's crystal form is one of the finest methods to identify it (external shape). This is referred to as cleavage.
Cleavage is the splitting of crystals along definite planes or axes. The word "cleave" means "to divide into flat pieces" or "to split." Cleavage can be either parallel (in equal parts) or perpendicular (at right angles) to the principal axis of the crystal. When a rock contains many small crystals, it is called a granitoid. If only one large crystal is present, it is called a monzogranite.
The word "granite" comes from the Greek word for "rock that splits into flat pieces," referring to the way certain types of granite look when cut into thin slices. Other names for this type of rock include gneiss, mica schist, and quartz schist.
Granites are formed when molten magma rises deep within the earth's crust until it reaches cooler layers of the planet's surface. As the hot liquid lava moves up through these layers, it solidifies into stone. The amount of heat that reaches the top of the volcano determines what kind of rock it will produce.
Color is easily visible and evident, although it is typically less accurate than other physical attributes. Texture is more difficult to see but extremely important in determining how you can use or process a mineral. The type of surface a mineral has affects how it interacts with other materials. For example, if a mineral has a rough surface, it will be harder to polish than one that is smooth.
The two most useful properties for identifying minerals are color and luster. Color helps identify minerals that look like things people know well (such as gold or silver). Luster identifies minerals that look like precious stones (such as topaz or zircon). It is also useful to know what part of the mineral gives away its identity. For example, if you were to find a piece of rock that was mostly black but had some white crystals mixed in, you could guess that it was probably quartz until you tested it. The white crystals would tell you for sure that you were right.
Some minerals have properties that are not useful for identification but are still important to know about. For example, some minerals are radioactive, which means they emit particles called alpha rays or gamma rays. These minerals include radium, uranium, and thorium.