Mineral Characteristics
Minerals abound in earth, but most people are probably aware of only a handful of these. Minerals are substances that occur naturally due to various geological processes. Minerals have specific chemical composition and physical properties together with a highly ordered atomic structure. The best way to study minerals in great detail is with a petrographic microscope.
The Difference between Rocks and Minerals
Rocks may be made up of several minerals but never vice versa. Sometimes, rocks may be largely composed of a single mineral. A good example of this would be limestone, which is almost completely made up of calcite. Minerals can be found all over the world but certain types of minerals may only be located in specific areas.
Identifying and Understanding Mineral Characteristics
A mineral may be identified according to its characteristics. Color, transparency, fracture, luster, hardness, specific gravity, tenacity, crystal form, cleavage, and crystal form are the most commonly used characteristics for mineral identification. Other notable characteristics of minerals include chatoyancy, conductivity, magnetism, burn test, streak, odor, and fluorescence.
Color – A mineral’s color is dependent on its chemical composition and is not entirely helpful in the process of identification. When describing color, you need not restrict yourself to naming a particular shade but you can also identify its intensity – such as whether it’s dark, light, or dull – and distribution, such as when it’s layered, splotchy, or streaked. You can also say if it’s metallic or not.
Luster – This characteristic describes a mineral’s surface when it’s viewed in the light. There are various words used to describe the luster of a mineral, but there is no standard way provided for describing this specific characteristic. A mineral may be, for instance, dull, glassy, or pearly.
Specific Gravity – This characteristic simply states if a mineral seems heavy or not.
Crystal Form – This describes what shape the mineral would grow into if it was allowed to grow in a cavity.
Cleavage – This refers to the patterns of breakage in a mineral. Cleavage may be described as the following: perfect 1 way refers to minerals that have broken on a perfect cleavage plane; perfect 2 ways result into stretched box-like figures; perfect 3 ways refers to those that have broken into rhombs while lastly, no cleavage refers to minerals with irregular breaks.
Tenacity – How tough is the mineral? If it breaks apart, what happens? Will it just break into pieces, split into two, crumble into dust, or change shape entirely? Minerals have different levels of tenacity. Some are elastic – no matter how you bend or pull it, they’ll still revert to their original shape when you’re done. Others are just tough while some are friable or easy to crumble.
Fracture – When there is no cleavage then there’s fracture present. Fractures may be jagged, conchoidal, splintery, or uneven.
Hardness – This characteristic refers to its ability to scratch and if it can be scratched by other minerals. Diamond is the hardest mineral of all; it is a precious stone with extremely high value. The Mohs’ scaleof hardness is generally used to measure the hardness of a given mineral.
Transparency – This refers to a mineral’s ability to transmit light. This is, however, dependent on several factors. Gemstones, which are considered precious materials, obtain higher value if they’re more transparent. There are standards provided for judging the transparency of gemstones but none for other types of minerals. In any case, one can simply describe minerals as either transparent if you an see through it completely, translucent if you can only see through it partially, and opaque if you can’t see through it at all.
Magnetism – Does the mineral have magnetic properties or not?
Chatoyancy – This is better known as cat’s eye and refers to an optical effect seen typically in chrysoberyl, quartz, beryl, moonstone, and a few other minerals. Gemstones also usually obtain higher market value because of this.
Fluorescence – Certain minerals fluoresce or appear differently under certain kinds of light.
Lastly, minerals can occasionally have distinctive odors as well as produce varying results when it comes to burn tests, streak, and conductivity.
Mineral Characteristics and the Petrographic Microscope
You can study these characteristics in greater detail when using a petrographic microscope. But first, make sure that the sample you have can fit your microscope’s stage. One with an inverted frame can accommodate larger samples. If it doesn’t fit, just take a thin section as a sample.
A normal microscope wouldn’t do when you are observing petrographic samples because it rarely comes equipped with a polarizer and analyzer, both of which are necessary to provide polarized light microscopy. Polarized illumination allows you to study samples with shiny surfaces without its reflection messing up the way your microscope’s own illumination system magnifies images of the sample.
For more information, please visit http://www.petrographic-microscope.com/
