Splendid Olivenite Crystals

Splendid Olivenite Crystals
Splendid Olivenite Crystals. Photo Tóth László
Olivenite is a copper arsenate mineral, formula Cu2AsO4OH. It crystallizes in the monoclinic system (pseudo-orthorhombic), and is sometimes found in small brilliant crystals of simple prismatic habit terminated by domal faces. More commonly, it occurs as globular aggregates of acicular crystals, these fibrous forms often having a velvety luster; sometimes it is lamellar in structure, or soft and earthy.

Olivenite is one of the most common minerals in the earth, and is a major rock forming mineral. Despite this, good specimens and large crystals are uncommon and sought after. Only few localities yield large examples of this mineral, although small and microscopic grains are found worldwide. Olivine is also found in meteorites, and large grains have been reported in many of them.

From Christiana Mine,Lavrion District Mines, Lavrion District (Laurion; Laurium), Attikí Prefecture (Attica; Attika), Greece

Color is dark olive green.
Luster is resinous to nearly adamantine.
Transparency: Specimens are translucent to almost opaque.
Crystal System is orthorhombic 2/m2/m2/m
Crystal Habits include crystals that are diamond-shaped, often acicular, prisms that are terminated by a dome with triangular faces. Can form feniform masses similar to wavellite's typical habit. Also as tiny crystalline druzes, fiberous masses, nodules and crusts.
Cleavage is poor in two directions, but rarely noticed.
Fracture is conchoidal.
Hardness is 3
Specific Gravity is approximately 3.9 - 4.4 (above average to heavy for translucent minerals)
Streak is olive green.
Associated Minerals are malachite, libethenite, Clinoclase, limonite, adamite, agardite and other secondary copper ore minerals.
Other Characteristics: Soluable in hydrochloric acid.
Notable Occurrences: Cornwall, England; Nevada, USA and Tsumeb, Nambia.
Best Field Indicators are color, habits, soluability in hydrochloric acid, associations, locallities and density.
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