Copper - an important ore & gem (sometimes)
"Arizona, our beautiful state, was built on mining".
- Jan Brewer
I wrote some book about mineralogy, and one about copper deposits; and it led me to the conclusion there are many copper deposits with dozens upon dozens of cupriferous minerals and cupriferous ores. The one thing about the many copper minerals found in the world is that many are brightly colored making identification a lot easier for the prospector and geologist. And, if you are looking for other types of ore - such as gold, silver, platinum group metals, lead, zinc, molybdenum and many others, copper is more abundant and usually mobilized with other important metals during pyrometamorphism and hydrothermal activity. This means when metals are put into motion by heat, pressure, and fluids, they seem to bunch together and become trapped near the earth's surface in structures, or by chemically favorable rocks. So, when you see copper, be sure you look for other nearby valuables.
In the West, copper is not unique: and you will find in all over the hills in old mining districts in Alaska, Arizona, California, Colorado, Idaho, Montana, Nevada, New Mexico, South Dakota, Oregon, Utah, Washington, Wyoming. You can spend a lifetime trying to collect all of the copper minerals, but when you get close, someone will identify a new one that was previously unknown. But the West is not unique, as many copper deposits have been found across Canada, Mexico as well as throughout the United States. In some places, there is such much copper, one could decorate a house or even a town with all of the copper. And for a lot of people, its hard to imagine so much copper and other metals and gemstones can be sitting right on the surface and much of it untouched and overlooked by others.
Some copper minerals are used as semi-precious gemstones, but many are soft and must be protected. Others produce spectacular collector specimens, decorative stones and lapidary. There are so many copper minerals that when I was in graduate school, one of my office mates built a reputation and PhD dissertation on identifying previously undocumented copper minerals. There are a few copper minerals that are more commonly used in gemstones and lapidary and these include turquoise, chrysocolla, malachite, azurite, native copper and cuprite.
In many of the Western States, the more one searches the mountain sides, the more copper minerals they will find, but in the copper state of Arizona - copper is literally everywhere! You will find it in the hills, basins, people's back and front yards and even in parking lots. The photo in the upper left is a boulder of azurite (blue), tenorite (black), dark red (cuprite) and minor malachite (green) from the Morenci, Arizona district. Imagine wearing that boulder as a pendant around your neck.
Although azurite (H=3.5 to 4), malachite (H=3.5 to 4), chrysolla (H=2.5 to 3.5) and tenorite (H=3 to 4) can produce extraordinarily specimens due to vivid color combinations, having a soft hardness precludes much use of these as gems because they are so easily scratched. Thus these and other soft copper minerals must be protected. Others such as turquoise (H=5 to 7) are more favorable for wear. Then there are the extremely colorful minerals such as covellite (H=1.5 to 2) and bornite (H=3 to 3.25) (also known as Peacock copper) that are unmatched in nature.
HOW TO IDENTIFY COPPER MINERALS
One distinct characteristic of copper minerals is a reaction to dilute (10%) hydrochloric acid. Copper carbonates such as azurite and malachite will fizz when they a few drops of hydrochloric (muriatic) acid are dropped on them; and most copper minerals will replace rusted iron with native copper when the copper is wetted with hydrochloric acid. Geologists pack around old beat up rock hammers and place a few drops of weak hydrochloric acid on a mineral suspected to contain copper. Next they rub their rock hammers in the wetted mineral. After it turns to mud on the rock hammer, they clean off the mud with their fingers, and if the mineral contains copper, rusty scratches in the rock hammer will be replaced by native copper.
Hausel (1997), The Geology of Wyoming's Copper, Lead, Zinc, Molybdenum and Associated Metal Deposits in Wyoming:Geological Survey of Wyoming Bulletin 70, 224 p., and
Hausel (2009), Gems, Minerals and Rocks of Wyoming. A Guide for Rock Hounds, Prospectors & Collectors. Booksurge, 175 p.
Hausel, 2014, A Guide to Finding Gemstones, Gold, Minerals and Rocks: Gemhunter Books, 367 p.
GemHunter Facebook page - lots of gems, minerals, rocks, field vehicles and jokes on my website.
Photo to the left shows a specimen with covellite (copper sulfide) from Butte Montana.