Minerals

• Minerals are naturally occurring solids that are usually inorganic, have an ordered, crystalline structure, and vary only slightly in their chemical composition.

• There are over 4,000 different minerals found on the earth, with more discovered each year.

• Only a few dozen of these minerals make up the vast majority of the rocks exposed on the Earth’s surface.

http://www.home4schoolgear.com/roandmikit.html

What makes minerals different?

• What makes one mineral different from another is it’s chemical make up. Scientist can identify one mineral from another using chemical tests. For example Quartz always has one atom of silicon for every two atoms of oxygen. For us, we need to use other ways to identify minerals.

The chemical content of most minerals only varies slightly within the sample. However, it only takes slight variations to produce significant color changes.

The following are all variations of the mineral quartz.

http://www.lemonquartz.com/lemon-quartz-gems.php

http://www.faceters.com/rough/quartz/index.shtmlImage Credit: Geological Survey of Canada photograph

Photo & Coll. G. Rüdlinger,SVSMF

http://dundee.rokpa.org/shop/index.php?cPath=35&osCsid=c7a5aa04841b66998914c57205c28413

The atomic structure determines most of the physical properties of minerals. To correctly identify a mineral you must rely on most or all of the following properties.

Physical Properties of Minerals• Luster• Density• Crystal faces• Hardness• Cleavage• Streak• Color

http://www.johnbetts-fineminerals.com/jhbnyc/diamdiag.htm

http://academic.brooklyn.cuny.edu/geology/grocha/mineral/cleavage.html

ColorColor is easily observed, but color alone provides

too little information to make an identification. As shown before, the same mineral can have several different colors, and several different minerals can have the same color. Below are three minerals that are all gold in color, but only one is actually gold.

http://www.minerals.net/mineral/elements/gold/gold1.jpg

http://www.california-gold-rush-miner.us/images/pyrite.jpg

http://skywalker.cochise.edu/wellerr/mineral/chalcopyrite/6chalcopyrite98.jpg

Streak

A streak test is one way to help identify a mineral. A streak test is when you rub the mineral on a white, unglazed piece of porcelain tile. What is left behind is the color of the mineral’s powder. Unlike color, the streak of a mineral does not vary. Sometimes the streak of a mineral is very different than its color.

http://meteorites.wustl.edu/id/streak.htmhttp://gwydir.demon.co.uk/jo/minerals/hematite.htm

Metallic hematite

http://www.cs.cmu.edu/~adg/images/minerals/o/magnetite1.jpg

Magnetite

Luster

Luster is how a mineral reflects light. It is one property used to help identify minerals. The main ways to classify luster are: metallic; glassy (vitreous); waxy, greasy or pearly; sub-metallic or dull; silky; earthy (resinous).

http://www.mineralogicalassociation.ca/young/images_page/luster.jpg

Density

• Density is the comparison of something’s mass to its volume. Finding a mineral’s density may help you determine what it is. Since rocks don’t come in convenient shapes, the easiest way to find a mineral’s volume is to put it in water. Then find its mass using a scale. Finally, divide the mass by the volume.

Density = mass/volume

Hardness• One of the best ways to determine a mineral’s

identity is to test its hardness. In1812, Friedrich Mohs invented a hardness scale for minerals. It ranks minerals on a scale from 1-10 based on ten different minerals. You determine the hardness number by scratching the mineral with different items.

http://www.infowest.com/life/mohs.gif

Crystal system• All minerals have

a crystal structure. Geologist divide minerals into 6 different groups based on the number and angle of the crystal’s faces.

http://www.geocities.com/asdfasdf23135/crystalsystem2.GIF

Fracture and Cleavage• How a mineral breaks

apart is one way you can tell them apart. If a mineral breaks easily along a flat line, it is said to have cleavage. If the mineral does not break apart easily or smoothly, it is said to have fracture. Fracture has several different classifications. Some are shell-shaped, hackly, and earthy.http://academic.brooklyn.cuny.edu/geology/grocha/mineral/cleavage.html