3.7" Siderite Crystals on Pyrite - Peru

Siderite, also known as "chalybite", is an iron carbonate mineral that belongs to the calcite group. It can contain a wide variety of impurities including manganese, magnesium, calcium, zinc and cobalt. Hues of brown are typical for siderite, with the occasional white and gray specimens. It can occur as rhombohedral crystals with rounded faces and in rare cases, it's found as scalenohedral crystals. Botryoidal, concretionary, massive, stalactitic and mammillary are some of the more common formations of siderite.

Being that siderite is such a prevalent mineral, it can be found all around the world in a wide variety of colors and formations. A noteworthy location that produces beautiful gemmy siderite specimens is the Morro Velho Mine in Minas Gerais, Brazil. The crystals collected from here are often translucent, yellow-green in color and form in association with dolomite, cubanite, pyrrhotite and chalcopyrite.

The chemical formula of siderite is FeCO3 with the variable formula including manganese, magnesium, calcite, zinc and cobalt ((Fe,Mg,Ca,Mn,Zn,Co)CO3).

The mineral pyrite or iron pyrite is commonly referred to as Fool's Gold because its metallic luster and pale brass-yellow hue give it a superficial resemblance to gold. In the old mining days, pyrite was sometimes mistaken for gold. Pyrite is the most common of the sulfide minerals with the chemical formula FeS2. Pyrite crystals occur in many shapes and habits, including cubes of all sizes, penetration twin cubes, pyritohedral clusters and as small druzy crystals that can exhibit a beautiful glistening effect.