process of identifying minerals?

Question

can anyone explain the process of identifying minerals to me?

Answer 1

There are over 4,000 known minerals. Each mineral has unique physical and chemical properties that distinguishes it from other minerals. Most geologists (or mineralogists) use color, streak, density, hardness, cleavage, habit, and luster to identify minerals.

More advanced techniques involve radioactivity, magnetic susceptibility, fluorescence, optical thin sections, X-ray diffraction, microprobe, and SEM.

There isn't really a "process" - most mineralogists have their own preferred methods, but elimination plays a key part. A mineralogist would look at a mineral with the naked eye, a hand elns, or a reflecting light microscope to determine its color, cleavage, hardness, and luster. For common minerals such as hornblende, quartz, calcite, mica, tourmaline, etc that is usually sufficient. If there is still some uncertainaty, the mineralogist could check its hardness and streak (if the mineral is large enough) and its density (or specific gravity) if the mineral can be separated from other materials. If that doesn't work, then s/he would make a thin section or do XRD testing.

Hope that helps!

Answer 2

JoAnna,

There is no one process that is used, and it depends a lot on the circumstances. From years of schooling, geologists are familiar with the appearance and properties of the most common minerals, and much of the time when they are out in the field looking at samples it simply takes a trained eye to look at the sample and determine what minerals are there. In situations where there are a small number of different possibilities, tests like a hardness test, streak test, cleavage, crystal shape, luster, and other unique properties help to narrow down the possibilities.

In a laboratory setting, in which you want to get exact answers with no guesswork, the most powerful tool is X-ray diffraction. A sample of the mineral is ground up into a powder and irradiated with X-rays, and the position of rays reflected to the other side is measured. The pattern of scattered X-rays is compared to a database of standard patterns for each mineral, and all of the minerals in the sample can be identified. A microprobe, which focuses a beam of electrons onto a tiny spot in a mineral and measures the types of X-rays it gives off, can be used to find the chemical composition of a mineral and is often used to identify it. In the old days (and a method still finds uses) you would shave off a thin piece of your sample and make a slide in order to examine the optical properties of the mineral under a microscope.

These are the most common processes used to identify minerals, but there are many more techniques and often a combination of them are used. It all depends on how much background knowledge you have and what tools you have available to you.