File:Native copper in sandstone (Nonesuch Formation, Mesoproterozoic; White Pine, UP of Michigan, USA) 2.jpg

English: Native copper in sandstone from the Precambrian of Michigan, USA. (public display, Geology Department, Wittenberg University, Springfield, Ohio, USA)

A mineral is a naturally-occurring, solid, inorganic, crystalline substance having a fairly definite chemical composition and having fairly definite physical properties. At its simplest, a mineral is a naturally-occurring solid chemical. Currently, there are about 5400 named and described minerals - about 200 of them are common and about 20 of them are very common. Mineral classification is based on anion chemistry. Major categories of minerals are: elements, sulfides, oxides, halides, carbonates, sulfates, phosphates, and silicates.

Elements are fundamental substances of matter - matter that is composed of the same types of atoms. At present, 118 elements are known. Of these, 98 occur naturally on Earth (hydrogen to californium). Most of these occur in rocks & minerals, although some occur in very small, trace amounts. Only some elements occur in their native elemental state as minerals.

To find a native element in nature, it must be relatively non-reactive and there must be some concentration process. Metallic, semimetallic (metalloid), and nonmetallic elements are known in their native state as minerals.

Copper is the only metallic element that has a "reddish" color - it’s actually a metallic orange color. Most metallic elements, apart from gold & copper, are silvery-gray colored. Copper tends to form sharp-edged, irregular, twisted masses of moderately high density. It is moderately soft, but is extremely difficult to break. It has no cleavage and has a distinctive hackly fracture.

The interesting copper-bearing specimen shown above comes from northern Michigan's White Pine Mine. Native copper was mined there from the 1950s to the 1990s. The host rocks are siliciclastic sedimentary rocks of the 1.07 to 1.08 billion years old Nonesuch Formation. At this locality, copper partially replaces rocks, occurs as fracture fillings, and occurs as scattered, small, intergranular masses. The rock shown here is sandstone with a couple copper-rich horizons. Copper mineralization occurred at 1.05 to 1.06 billion years ago, after deposition of the sediments.

Stratigraphy: Nonesuch Formation, middle Oronto Group, upper Keweenawan Supergroup, upper Mesoproterozoic, ~1.07 to 1.08 Ga

Locality: White Pine Mine, Ontonagon County, eastern side of the Porcupine Mountains, northwestern Upper Peninsula of Michigan, USA (vicinity of 46° 45' 53.04" North latitude, 89° 33' 44.98" West longitude)

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Photo gallery of copper:

www.mindat.org/gallery.php?min=1209