Sarabauite

Chemical formula: CaSb₃+₁₀O₁₀S₂-₆

Sarabauite is a rare antimony-calcium sulfate-oxide mineral, forming prismatic, almost black crystals with a metallic luster.

## Characteristics Sarabauite is a complex antimony-calcium sulfate-oxide mineral. It occurs as elongated, prismatic crystals, which can reach up to 2 cm in length. They are usually longitudinally striated. Its appearance is very distinctive – it has a dark red to almost black color and a strong, metallic or submetallic luster, giving it an appearance similar to stibnite. ## Physical Properties This mineral is characterized by a hardness of approximately 4 on the Mohs scale. It is brittle and has an uneven fracture. Its density is quite high, around 5.43 g/cm³. The luster is metallic to submetallic. It is an opaque mineral. ## Colors and Varieties Sarabauite occurs in a uniform, dark red color, which can appear almost black in reflected light. No color varieties or commercial varieties are known. ## History and Name The mineral's name comes from its discovery locality – the Sarabau Mine (also known as Krach Mine) in the Bau District, Sarawak State, Malaysia, on the island of Borneo. It was first described in 1977 by I. Nakai, H. Adachi, and K. Nagashima. ## Applications Due to its extreme rarity, sarabauite has no industrial applications. It is solely an object of interest for collectors specializing in rare minerals and for scientific institutions.

Properties

Mohs hardness: 4
Luster: Metallic, Sub-Metallic
Streak: Red-brown
Density: 5.43
Cleavage: None
Fracture: Uneven
Transparency: Opaque
Crystal system: Monoclinic

Diagnostic features

## Identification Sarabauite can be identified by its characteristic habit of long, prismatic crystals, dark red to black color, metallic luster, and longitudinal striations on crystal faces. High density is also a helpful feature. A reddish-brown streak is a key characteristic distinguishing it from visually similar minerals. ## Distinguishing from Similar Minerals Sarabauite is sometimes confused with stibnite, which has a similar habit and metallic luster. However, stibnite has a lead-gray color and streak, and is also much softer (hardness 2) and possesses perfect cleavage, which sarabauite lacks. It is distinguished from other dark, prismatic minerals by the combination of color, luster, hardness, and reddish-brown streak. ## Crystal Forms Sarabauite crystals are monoclinic and have a prismatic habit, often strongly elongated along one axis. Distinct, longitudinal striations are almost always visible on the crystal faces. It rarely forms aggregates, most often occurring as single crystals embedded in the host rock.

Geological environment

## Genesis Sarabauite is a hydrothermal mineral. It forms in low-temperature calcite veins that cut through limestones. Its formation is associated with the activity of antimony- and sulfur-rich solutions. ## Mineral Associations This mineral co-occurs with calcite, stibnite, realgar, native sulfur, and quartz. At its type locality (Sarabau, Malaysia), it was found in association with these very minerals. ## Localities The only confirmed and well-documented occurrence of sarabauite in the world is its type locality – the Sarabau Mine in Sarawak State, Malaysia. It is an endemic mineral to this single locality.

Rarity

Extremely rare

For collectors

## Quality Criteria The most prized sarabauite specimens are those with well-formed, sharply terminated, and undamaged crystals with a distinct luster. Crystal size is important – specimens with crystals exceeding 1 cm are considered exceptional. Contrast with a light, calcitic matrix significantly enhances the visual appeal and value of the specimen. ## Popular Localities The only source of collector specimens is the historical type locality in the Sarabau Mine in Malaysia. This mine is no longer active, meaning new specimens do not enter the market, and those available come from old collections.

Care and storage

## Cleaning Sarabauite specimens should be cleaned very carefully, preferably using compressed air to remove dust. If wet cleaning is necessary, use only distilled water and a very soft brush, avoiding strong rubbing. After contact with water, the specimen should be immediately and thoroughly dried. ## What to Avoid Avoid contact with all chemicals, including acids and detergents. The mineral is brittle, so protect it from impacts and falls. Do not heat it or subject it to ultrasonics. Prolonged exposure to moisture can be harmful. ## Storage Sarabauite specimens are best stored in stable conditions, in closed collector boxes or display cases, away from dust, moisture, and direct sunlight. It is advisable to isolate it from other minerals to prevent scratches.

External references

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