Ferrobustamite
Chemical formula: CaFe<sup>2+</sup>Si<sub>2</sub>O<sub>6</sub>
Ferrobustamite is a rare, iron-rich silicate from the wollastonite group, forming fibrous or platy crystals in metamorphic rocks called skarns.
Properties
- Mohs hardness
- 5.5-6.5
- Luster
- Vitreous
- Streak
- White
- Density
- 3.43-3.46
- Cleavage
- Perfect on {100}, Good on {001} and {10-2}
- Fracture
- Uneven to Conchoidal
- Transparency
- Translucent to Opaque
- Crystal system
- Triclinic
Diagnostic features
## Identification Ferrobustamite is most easily recognized by its characteristic occurrence environment – skarns. Its fibrous or elongated habit, greenish-brown color, vitreous luster, and perfect cleavage are key visual features. It often forms radial aggregates. ## Distinguishing from Similar Minerals Ferrobustamite can be confused with other skarn silicates. From bustamite, its manganese analogue, it usually differs by the absence of pink hues and is difficult to distinguish without chemical analysis (Fe > Mn). From wollastonite, it is most often distinguished by its greenish or brownish color (wollastonite is usually white or gray) and higher density. Hedenbergite, also a green skarn pyroxene, has a different cleavage angle (approximately 87°), whereas ferrobustamite has cleavage typical of pyroxenoids. ## Crystal Forms Crystals are platy, bladed, or fibrous, often elongated. They usually occur as radial, fan-shaped, or tangled aggregates. Isolated, well-formed crystals with distinct faces are rare.
Geological environment
## Genesis Ferrobustamite is a typical mineral of contact metamorphic rocks, known as skarns. It forms at high temperatures as a result of metasomatism at the contact between magmatic intrusions (usually granitoid) and calcium-rich sedimentary rocks, such as limestones and dolomites. ## Mineral Associations This mineral often coexists with other skarn minerals, such as hedenbergite, diopside, andradite, vesuvianite, wollastonite, as well as sulfides, e.g., galena and sphalerite. ## Localities Key ferrobustamite localities worldwide include the type locality at Granite Gap in New Mexico (USA), Obira Mine in Oita Prefecture (Japan), Dalnegorsk deposit in Siberia (Russia), and the Broken Hill area in New South Wales (Australia).
Rarity
Rare
For collectors
## Quality Criteria Specimens with well-formed, sharp crystals of intense, green color are most valued by collectors. Radial aggregates forming aesthetic shapes enhance their appeal. Specimens where ferrobustamite occurs alongside other skarn minerals of contrasting colors, such as dark green hedenbergite, brown andradite, or metallic sulfides, are also highly regarded. ## Popular Localities Specimens of the highest collector value come from classic skarn localities, such as the Obira Mine in Japan and Dalnegorsk in Russia, which have yielded large and well-formed crystals and aggregates.
Care and storage
## Cleaning Ferrobustamite specimens should be cleaned gently, using a soft brush and distilled water. Short soaks can be used to remove loose contaminants. Ultrasonic cleaners should be avoided, as they can damage the mineral along its cleavage planes. ## What to Avoid The mineral is sensitive to strong acids, which can etch it. It should be protected from impacts and falls, as its perfect cleavage makes it prone to breaking. It is not particularly sensitive to light, but prolonged exposure to extreme conditions may not be advisable. ## Storage Collector specimens of ferrobustamite are best stored in individual, padded boxes or display cases to prevent abrasions and mechanical damage. Isolation from dust and humidity will help preserve the mineral's natural luster.