Gems, Jewels and other shiny stones. There are too many to list all of them so I will select a sample of useful or popular stones. I will start with the obvious jewel the diamond. Most people know that diamond are pure carbon, not so many people know that diamond can burn and dissolve. Forming carbon into diamonds requires heat and pressure, but too much heat and the carbon will burn. For these reasons diamond are mostly found in mines, but of course do appear on the surface in the pipe where they formed... usually. There was a diamond rush in Wisconsin until it was realized that the diamond pipe was actually in Canada and the diamonds were relocated by the glaciers during the ice age. Speaking of glaciers, ice is a mineral and can be quite valuable especially in warmer climates. Ice can be mined from glaciers or frozen lakes. The ice blocks are then packed in sawdust and put in ice houses for the summer. Ice from natural sources was a valuable commodity until well the 1920's.
Amber is another exception to the valuable stone rule. Amber is not really a stone but is petrified tree resin. Amber is a lot more common than you might think. Amber is often found with coal but the grains are usually sand sized and not worth anything (more on coal in another post). Amber is not always.. well... amber in color. It can come in shades of blue, red or black as well. While mostly used for jewelry, amber has also been used as a medicine and in perfume.
Quartz, is the second most common mineral on earth. It is found with... you guessed it, granite. Chemically quartz is SiO4 which forms a clear crystal, but impurities can give quartz different colors and properties. Varieties of quartz include: rose quartz, tiger eye, amethyst, citrine, agate and many more. Quartz crystals of unusual size and clarity are thought by some to have magical properties and my be used in some types of healing.
Jade is actually two different rocks. Nephrite and jadite, they are both metamorphic silica minerals. Jade comes in a wide variety of colors, but green is the most well known. It is usually weathered out of... not granite. Jade is a metamorphic rock and granite is not. But, granite or sedimentary rocks can be metamorphosed into gneiss (nice) and that is where jade is found (as well as garnets). Jade was/is used for its mystical properties as well as in art and jewelry.
Rubies are cool because we don't know exactly how they form in nature. Rubies are a form of corundum and are made from aluminum oxygen a touch of chromium (for color) They form where there is little silica (the most abundant mineral) and iron (the most abundant metal). They are most often found in marble deposits. Rubies are slightly fluorescent. Under UV light (like in sunlight) they give off more visible light than they absorb. Burmese warriors would imbed rubies under their skin so they would be immune to injuries in battle. Rubies were also used in medicine for flatulence, stomach pains and indigestion.
Sapphires are similar to rubies, take out the chromium and add a bit of titanium, magnesium, copper or iron for color. They come in colors from red to yellow and blue. They are found in alluvial deposits. Sapphires do not erode easily so they fall out of the rock matrix where they formed and drift down stream until they are deposited in a loose matrix (alluvial deposit). They may be found with gold, platinum or other gem stones (a valuable alluvial deposit is also known as a placer deposit).
I think those are the major ones.
Thanks Waldronate, I typed a bit to slow and we got some overlap but that is cool. I forgot about hydrothermal vents as a mineral source.
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