Answer:
When a geologist studies the characteristics of rocks, this specialist will look for these qualities, and with them, he/she will classify minerals and the rocks in which these minerals are found. These qualities are: hardness, specific gravity, luster, color, streak, cleavage, fracture and tenacity. These are some of the most important qualities looked for in rocks when a geologist wants to classify and study them.
In the case of hardness, what geologists look for is how much will one mineral resist being damaged, or scratched, when rubbed by another. In order to identify this quality, geologists can use a table that gives values to how easily, or hardly, is a mineral scratched when hit with another.
In the case of luster, what geologists look for is the reflection of light, or how much light is reflected by a mineral. As such, there are two classifications in this category, and they are metallic, and non-metallic and those minerals that do not reflect light at all, are referred to as "dull" or "chalky".
Streak, finally, is another category used, and it evaluates the color that a mineral produces when turned to dust, or powder. In order to do this, geologists use something called a streak plate and they rub the mineral against it. The streak that is left by the mineral, and its color, are thus identified and classified.
These are, in summary, some of the many ways in which geologists classify rocks and minerals.
