Scorodite

Chemical formula: Fe₃+As₅+O₄·₂H₂O

Scorodite is a hydrated iron arsenate, forming small, vitreous crystals with a wide range of colors, from green to purple.

## Characteristics Scorodite is a hydrated iron arsenate, valued by collectors for its attractive crystals and diverse colors. It most commonly occurs as small, well-formed crystals with a bipyramidal or tabular habit, forming crusts and druses. It is also found as earthy, radial, spherical, or botryoidal aggregates. Its crystals are characterized by a strong luster, from vitreous to almost adamantine. ## Physical Properties This mineral is relatively soft, with a Mohs hardness of 3.5-4. It is brittle and has a density in the range of 3.27-3.33 g/cm³. Crystals can be transparent to translucent. A characteristic feature, though destructive to the specimen, is the emission of a garlic odor when heated, which is typical for arsenic minerals. ## Colors and Varieties Scorodite exhibits a wide palette of colors. The most common shades are grayish-green, yellowish-brown, and pale violet-blue. Colorless, white, yellow, brown, and even intensely blue or purple specimens, which are particularly sought after, also occur. The color of the mineral can change under the influence of temperature. No commercial varieties are distinguished, and classification is mainly based on color and form. ## History and Name The name scorodite, given in 1818 by the German mineralogist J.F.A. Breithaupt, comes from the Greek word *skorodon* (σκοροδον) meaning "garlic". This refers to the characteristic odor emitted by the mineral when heated, resulting from the volatilization of arsenic. ## Uses Scorodite is primarily a mineral of collector's interest. Due to its arsenic content, it can be a minor ore of this element, but it is rarely exploited for this purpose. It is sometimes used as an indicator mineral during the exploration for ore deposits rich in arsenic.

Properties

Mohs hardness: 3.5-4
Luster: Vitreous to subadamantine
Streak: White
Density: 3.27-3.33
Cleavage: Imperfect on {100} and {011}
Fracture: Conchoidal to uneven
Transparency: Transparent to translucent
Crystal system: Orthorhombic

Diagnostic features

## Identification Scorodite can be identified by its characteristic crystal shape (short, prismatic, or bipyramidal), strong, vitreous luster, and typical colors (greenish, bluish, brownish). Its occurrence in the oxidation zones of arsenical deposits is a key indicator. The garlic odor test upon heating is diagnostic but destructive to the sample and dangerous. ## Distinguishing from Similar Minerals Scorodite is sometimes confused with variscite, which, however, has a lower density, is a phosphate, and does not emit a garlic odor. Adamite often exhibits a stronger, yellowish-green color and fluorescence under UV light, which scorodite usually lacks. Pharmacosiderite, another iron arsenate, crystallizes in the isometric system, forming characteristic cubic crystals. ## Crystal Forms It crystallizes in the orthorhombic system. It most often forms pseudo-octahedral, bipyramidal, or tabular crystals. It occurs as druses and crystal aggregates, as well as in radial, botryoidal, earthy aggregates, and as massive crusts.

Geological environment

## Genesis Scorodite is a secondary mineral, formed in the oxidation zones (gossans) of hydrothermal ore deposits rich in arsenic minerals, mainly arsenopyrite. It forms as a result of chemical weathering of primary sulfides and arsenides under oxygenic conditions. ## Mineral Associations It often co-occurs with the minerals from which it formed, such as arsenopyrite, as well as with other products of their oxidation, such as pharmacosiderite, beudantite, jarosite, goethite, and limonite. It can also be associated with quartz, fluorite, and various sulfates. ## Localities Exceptional quality purple and blue crystals come from the mine in Hezhou (Guangxi, China). Historically important specimens are from Tsumeb in Namibia, Djebel Debar in Algeria, and Saxony in Germany. Beautiful specimens have also been found in mines in Mapimí (Durango, Mexico), Cornwall (United Kingdom), as well as in Utah and Nevada in the USA, and Minas Gerais in Brazil.

Rarity

Not very common

For collectors

## Quality Criteria The most highly prized scorodite specimens are characterized by sharp, well-formed crystals with high transparency and strong luster. Color is a key factor – intensely blue, purple, and emerald-green crystals command the highest prices. The size of the crystals and their placement on an aesthetic, contrasting rock matrix are also important. Undamaged specimens are significantly more valuable. ## Market Prices Scorodite prices vary widely. Small crusts or microcrystals can be acquired for small amounts. Prices for miniature specimens with well-formed crystals start from a few tens of dollars, while high-grade cabinet specimens from classic localities, with large, intensely colored crystals, can cost from several hundred to many thousands of dollars. ## Popular Localities The best specimens in the world are currently considered to be those from Hezhou, China, known for their unusual purple and blue colors. Classic scorodites, prized by collectors, come from Tsumeb, Namibia (diversity of forms and colors) and Mapimí, Mexico (often in the form of attractive spherical aggregates).

Care and storage

## Cleaning Scorodite specimens should be cleaned very carefully, using a soft brush and distilled water. Due to its brittleness and relatively low hardness, ultrasonic cleaners and strong friction should be avoided. ## What to Avoid Scorodite is an arsenate, which means it is toxic. Inhaling dust should be avoided, and hands must be thoroughly washed after any contact with the mineral. It should not be heated, as it emits toxic arsenic fumes. It is sensitive to acids. Some specimens may be sensitive to prolonged exposure to sunlight. ## Storage It is recommended to store scorodite in closed, labeled containers or display cases to limit contact with dust and moisture and to prevent accidental ingestion. It should be kept away from heat sources and direct sunlight, in a place with stable temperature.

External references

https://en.wikipedia.org/wiki/https%3A%2F%2Fen.wikipedia.org%2Fwiki%2FScorodite