Rocks and Minerals
Simply speaking, minerals are naturally occurring inorganic compounds. They are the building blocks of all rocks. A rock can be made up of one or more minerals.
Pyrite Cluster
The mineral pyrite is sometimes called "fools gold" because its shiny appearance can fool amateur prospectors. This particular specimen has large, well defined crystal faces that display prominent striations.
Apophyllite
Apophyllite, a type of zeolite mineral, forms inside cavities in igneous rock.
Ventifact, Dreikanter
Ventifacts are rocks that have been shaped by the erosive power of wind blown sediment. When a rock sits in one place in an area where strong winds blow abrasive sediment such as sand, the rock can become faceted on its upper surface. If measured in place, the direction of these facets can reveal information about the dominant wind directions in the area. The term dreikanter refers to a ventifact that has three ridges, and therefore has been etched by sediment that had been blown by multiple wind directions.
Olivine Crystals
These olivine crystals formed in volcanic rock rich in iron and magnesium. Although olivine is a relatively common mineral deep within the earth, crystals like these do not usually last long on the surface of the earth due to their tenancy to breakdown chemically when exposed to weather. The gemstone peridot is an exceptionally high-quality variety of the mineral olivine.
Banded Iron Formation
Paleoproterozoic (1.8 Billion years old)
The Earth didn’t always have the oxygen rich atmosphere we breathe today. During the Precambrian, the composition of Earth’s atmosphere was very different. There was no oxygen. The chemistry of the world’s oceans was also different. Ancient ocean water reduced and dissolved many tons of iron.
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This all changed as oxygen-producing cyanobacteria slowly began to add oxygen to Earth’s atmosphere over hundreds of millions of years. The oxygen became dissolved in oceanwater, and reacted with the iron causing it to oxidize and rust. Iron oxides precipitated out of the seawater causing huge deposits of iron oxide to form at the bottom of shallow seas during a period in geologic time called the Paleoproterozoic. This is known as the Great Oxygenation Event.
The iron that settled to the bottom of shallow seas formed alternating layers of iron oxides such as hematite, and red chert (jasper). These iron rich layers are called banded iron formations.
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These examples come from the area of the Jerome Arizona mining district. Banded iron formations are found within the same marine sediment sequence that hosts the volcanogenic massive sulfide deposits that were mined from the late nineteenth century through the mid twentieth century.
