Cebollite
Chemical formula: Ca<sub>5</sub>Al<sub>2</sub>(SiO<sub>4</sub>)<sub>3</sub>(OH)<sub>4</sub>
Cebollite is a rare calcium aluminum silicate, forming aggregates of fibrous, white or greenish crystals.
Properties
- Mohs hardness
- 5
- Luster
- Vitreous, Silky
- Streak
- White
- Density
- 2.93
- Cleavage
- Good on {100}
- Fracture
- Uneven
- Transparency
- Translucent to opaque
- Crystal system
- Orthorhombic
Diagnostic features
## Identification Cebollite is most easily recognized by its characteristic, radial-fibrous aggregates with a silky luster. Its white or pale green color and relatively low hardness (5 on the Mohs scale) are also helpful indicators. It occurs in a specific geological environment, in contact zones between igneous rocks and limestones. ## Distinguishing from Similar Minerals Cebollite is sometimes confused with other white, fibrous minerals such as wollastonite, pectolite, or tremolite. Wollastonite is usually harder and often exhibits fluorescence under UV light, which cebollite does not possess. Pectolite is harder and denser. Final differentiation from these minerals often requires advanced studies, e.g., by X-ray diffraction (XRD) method. ## Crystal Forms Cebollite crystals are prismatic or acicular, elongated along one axis. They almost always occur as radial or tangled fibrous aggregates. Less commonly, they form compact or massive aggregates.
Geological environment
## Genesis Cebollite is a low-temperature hydrothermal mineral. It forms in contact zones where igneous rocks (e.g., diabases, nepheline syenites) interact with carbonate rocks, such as limestones and marbles. It forms as a result of contact metasomatism, often in veins cutting through altered rocks. ## Mineral Associations This mineral often co-occurs with other minerals typical of skarns and contact zones. The most common associations include: vesuvianite, garnets (mainly grossular), diopside, foshagite, wollastonite, melilite, titanite, perovskite, and calcite. ## Localities The most important and classic locality for cebollite is Cebolla Creek in Gunnison County, Colorado, USA. It is also known from Iron Hill in the same county. Other reported localities worldwide include Riverside County in California (USA); the Ilimaussaq igneous complex in Greenland; the vicinity of Boisséjour in France; Mount Dupeze in Quebec (Canada); and in the volcanic rock complex on Fuerteventura Island (Canary Islands, Spain).
Rarity
Rare
For collectors
## Quality Criteria The most valued specimens by collectors are those with well-formed, radial aggregates exhibiting a distinct silky luster. Color purity is important – purely white or delicately greenish specimens are preferred. Contrast with a dark matrix significantly enhances the visual appeal of the specimen. Due to its rarity, even small but well-defined aggregates are sought after. ## Popular Localities By far the most classic and desirable specimens come from the type locality at Cebolla Creek in Colorado, USA. Material from this location is historically most important and serves as a reference point for collectors of this mineral.
Care and storage
## Cleaning Cebollite specimens should be cleaned very carefully, using a soft brush to remove dust. Due to its fibrous nature and low hardness, avoid washing under running water, which could damage delicate aggregates. If liquid is necessary, a brief immersion in distilled water is recommended, followed by thorough drying in a stream of cool air. ## What to Avoid Avoid contact with acids and other chemicals that may react with the mineral. Cebollite is susceptible to mechanical damage, so it must be protected from impacts, scratching, and abrasion. It should not be heated or exposed to prolonged strong light. ## Storage Cebollite specimens are best stored in separate, padded collector boxes to prevent contact with harder minerals. Delicate, fibrous aggregates require special protection from dust and physical damage, so it is recommended to keep them in closed display cases or "micromount" containers.