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STIBICONITE:

PHYSICAL CHARACTERISTICS:

Color is white or gray but usually tinted brown or yellow.

Luster is earthy.

Transparency crystals are opaque.

Crystal System is isometric, possibly.

Crystal Habits: include the earthy masses and crust but well known for its stibnite pseudomorphs showing a sword-like bladed habit, singular or in radiating clusters.

Cleavage none

Fracture is earthy

Hardness is 4 - 5.5.

Specific Gravity is 3.5 - 5.9 (above average to heavy)

Streak is white.

Associated Minerals include stibnite, valentinite, and other antimony oxides.

Other Characteristics: a white coating may appear on specimens with time (don't try to remove).

Notable Occurrences include Goldkronach, Germany; Wolfe County, Quebec; San Luis Potosi, Mexico; Nevada, USA and Huaras, Peru.

Best Field Indicators are stibnite-like crystals, color, luster, hardness and density.

Stibiconite is a rather rare mineral, but is known among collectors for its first class pseudomorphs. A pseudomorph is an atom by atom replacement of one mineral's chemistry to form another completely different mineral. The process leaves the crystal shape of the lost mineral intact. Pseudomorph means false (pseudo) shape (morph). In the case of stibiconite, the mineral that is lost is stibnite, Sb2S3. Stibnite's sword-like crystals arranged in radiating clusters are truly works of natural art. A pseudomorph of stibiconite can perfectly match the sword-like shape of stibnite's crystals. It can do this because the process is done slowly, allowing the oxygens to replace the sulfurs essentially one atom at a time. However, stibiconite lacks the metallic luster or steel gray color of stibnite. If two classic specimens of the minerals are put side by side the color and luster contrasts along with the similarity of the crystal shapes would simply fasinate the onlooker.

As might be guessed, stibiconite forms in the oxidation zone of antimony sulfides. The oxygens oxidize a portion of the antimonies (Sb) from +3 (as in stibnite) to +5. The two different valences occupy different sites in the structure of the mineral, since the size of the atoms diminsh greatly when reduced in charge. To represent this, the formula could be written as so, Sb(+3)Sb(+5)2O6(OH). This formula more closely fits the general formula for the Stibiconite Group, M1 - 2X2O6(O, OH, F).

Some of the finest stibiconites, producing wonderful pseudomorphs, occur in a few new antimony mines that have yet to produce any unaltered stibnite clusters. It is hoped that these mines will break through the oxidation layers into some pockets of amazingly stunning stibnite specimens. These stibiconites, although in their own right magnificent, only tease the stibnite collectors as to what once was there.

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