Identifying Rocks – M

By looking at and using a few simple tests, you can get an idea of which rock or mineral you have.  Here are some characteristics to look for.

1) What color is your rock or mineral?

Different rocks and minerals are composed of different elements and chemicals.  Because of this, color can vary greatly from one rock/mineral to another.  It is important to consider the environment the rock has been in, however.  Weathering and exposure to other chemicals can change the color of the rock/mineral.  Color CAN be used to help identify a rock, but it is not the best way.

2) Does the rock/mineral reflect light?

The way the rock or mineral reflects light is referred to as LUSTER.  Is the surface very reflective (like a metal)?  Is it shiny like glass?  Does it have a pearl-like appearance?  Maybe it is dull and does not reflect light at all?

3) How hard is your rock/mineral?

You can test this by comparing how your rock scratches other surfaces.  You can also explain how easy it is to scratch your rock/mineral.    There is a scale called the Mohs Hardness Scale that compares the hardness of common rocks/minerals. You can look at this one for reference.

4) If you rub the rock/mineral across a surface like a concrete sidewalk, what mark does it make?

The mark or color left behind when you rub the rock/mineral against a rough surface is called the STREAK.

5) Describe the way your rock/mineral breaks.

Some rocks or minerals will break in sheets.  Some break into chunks like cubes.  Some will break leaving jagged edges.  The word used for this characteristic is CLEAVAGE.

6) Does the rock react if you expose it to an acid (like vinegar)?

Applying an acid to a rock/mineral can help identify which chemicals the rock is composed of.  Some materials in a rock/mineral, like calcium, will react and bubble when exposed to acids.

There are several other characteristics scientists look at when studying rocks and minerals.

One is called specific gravity and it describes the density of the rock or mineral. (The density is a comparison of the rock/mineral’s weight compared to the weight of an equal volume of water.)  Gold and silver are very heavy.  There are even rocks that are less dense than water (which means they can float), like pumice.

Other characteristics to observe would be the formation of crystals and the transparency.  There are some unique characteristics, typically found in rare rocks/minerals, like magnetism and odor.  There are even rocks that will “glow” when exposed to UV light.