Ambrinoite

Chemical formula: [K,(N<sup>3-</sup>H<sub>4</sub>)]<sub>2</sub>(As<sup>3+</sup>,Sb<sup>3+</sup>)<sub>6</sub>(Sb<sup>3+</sup>,As<sup>3+</sup>)<sub>2</sub>S<sup>2-</sup><sub>13</sub>·H<sub>2</sub>O

An extremely rare arsenic, antimony, and potassium sulfide, forming acicular crystals of intense red color.

## Characteristics Ambrinoite is a very rare, complex sulfide (sulfosalt) of arsenic, antimony, potassium, and ammonium. It occurs as microscopic, acicular or fibrous crystals, which usually form radial or tangled aggregates. Individual crystals rarely exceed 1 mm in length. Its most characteristic feature is its intense red to reddish-orange color. ## Physical Properties This mineral is characterized by a strong, adamantine luster. It is translucent. Its Mohs hardness has not yet been determined due to the small size and rarity of the crystals. The density calculated based on chemical composition and crystal structure is 3.86 g/cm³. ## Colors and Varieties Ambrinoite occurs in a uniform, bright red to reddish-orange color. No color or commercial varieties are known. ## History and Name The mineral is named in honor of Joseph Ambrino (1940–2010), a professor of chemistry at the University of Southern California, in recognition of his contributions to sulfosalt research. Ambrinoite was described as a new mineral species in 2012 by Werner H. Pinch and Andrew C. Roberts based on material obtained from the Getchell mine in Nevada. ## Applications Due to its extreme rarity and microscopic size, ambrinoite has no industrial applications. It serves solely as an object of scientific research and a valuable specimen for specialized micromount mineral collectors.

Properties

Luster
Adamantine
Streak
Orange-yellow
Density
3.86
Transparency
Translucent
Crystal system
Monoclinic

Diagnostic features

## Identification Identification of ambrinoite is extremely difficult and practically impossible without advanced analytical techniques, such as X-ray diffraction (XRD) or electron microprobe analysis. Visual features that may suggest its presence are radial aggregates of fine, acicular crystals of bright red color and adamantine luster, occurring in paragenesis with other rare sulfosalts. ## Distinguishing from similar minerals Ambrinoite can be confused with other red, acicular minerals from the same locality, mainly getchellite and laffittite. Getchellite has a slightly different crystal habit and hue, and laffittite is more orange. Definitive differentiation of these minerals requires specialized laboratory analysis. ## Crystal forms It forms very fine, slender crystals with an acicular or fibrous habit. These crystals most often occur as radial or chaotically tangled clusters and aggregates.

Geological environment

## Genesis Ambrinoite is a hydrothermal mineral, crystallizing at very low temperatures. It forms in voids and fractures within arsenic- and antimony-rich sulfide ores, associated with Carlin-type gold deposits. ## Mineral associations This mineral occurs in direct proximity to getchellite, realgar, orpiment, stibnite, and other rare sulfosalts such as laffittite and cristite. ## Localities The only confirmed occurrence of ambrinoite in the world is its type locality - the Getchell mine in Humboldt County, Nevada, USA.

Rarity

Extremely rare

For collectors

## Quality criteria As a micromount mineral, specimens with clearly formed, rich crystal groups are most highly valued. Key criteria include the intensity and purity of the red color, the sharpness and luster of the acicular crystals, and an attractive composition with other rare minerals from this locality, e.g., crystalline getchellite. ## Popular localities The only collectible specimens come from the Getchell mine in Nevada. This is the only source of this mineral in the world, and material is extremely difficult to obtain.

Care and storage

## Cleaning Due to the exceptional rarity and delicacy of specimens, cleaning is highly discouraged. If absolutely necessary, only a gentle stream of compressed air can be used to remove dust. Avoid contact with water, ultrasound, and any chemical agents. ## What to avoid As a sulfosalt, ambrinoite is potentially sensitive to prolonged exposure to light, which can cause fading or surface decomposition. It should be protected from high temperatures, humidity, and sudden changes in environmental conditions. Contact with acids or detergents will cause its destruction. ## Storage Ambrinoite specimens should be stored under stable conditions, in a dark and dry place. The best solution is a tightly sealed micromount box, which protects the mineral from dust, mechanical damage, and changes in humidity.

Sources

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