Woodhouseite
Chemical formula: CaAl<sub>3</sub>(S<sup>6+</sup>O<sub>4</sub>)(PO<sub>4</sub>)(OH)<sub>6</sub>
Woodhouseite is a rare mineral from the phosphate, sulfate, and arsenate group, forming small, pseudocubic or rhombohedral crystals with a vitreous luster.
Properties
- Mohs hardness
- 4.5
- Luster
- Vitreous, Pearly
- Streak
- White
- Density
- 3.012
- Cleavage
- Perfect on {0001}
- Fracture
- Uneven
- Transparency
- Transparent to translucent
- Crystal system
- Trigonal
Diagnostic features
## Identification A characteristic feature of woodhouseite is its small, sharp, pseudocubic or rhombohedral crystals. The combination of such crystal forms with a hardness of 4.5, vitreous luster, and occurrence in specific hydrothermal environments or oxidation zones is key for identification. ## Distinguishing from Similar Minerals Woodhouseite can be confused with other minerals from the beudantite group, such as svanbergite or corkite. Distinguishing them without advanced chemical (EDS) or X-ray (XRD) analyses is often impossible. It may also resemble some zeolites or feldspars, but differs from them in hardness and paragenesis. ## Crystal Forms Most often, it forms single, well-formed rhombohedral crystals, often modified in such a way that they resemble cubes (pseudocubic). Crystals are usually small, rarely exceeding a few millimeters. It also occurs in granular aggregates.
Geological environment
## Genesis Woodhouseite is a secondary mineral, formed as a result of hydrothermal processes or in the oxidation zones of ore deposits. It forms in quartz veins and pegmatites, often in the presence of other phosphate and sulfate minerals. It can also form in aluminum-rich sedimentary rocks that have been subjected to solutions containing phosphates and sulfates. ## Mineral Associations This mineral often co-occurs with minerals such as topaz, augelite, lazulite, pyrophyllite, barite, quartz, diaspore, kaolinite, alunogen, and wavellite. ## Localities The most important locality, which is also the type locality, is the Champion Sillimanite (Champion Spark Plug) Mine in the White Mountains, Mono County, California, USA. Other known localities include the Willard Mine in Pershing County, Nevada, USA; the St. John's Mine in Tooele County, Utah, USA; as well as occurrences in Peru, Brazil, and Slovakia.
Rarity
Rare
For collectors
## Quality Criteria The most valued by collectors are specimens with sharp, well-formed, and clearly visible crystals, set on a contrasting rock matrix. Specimens with unusually colored (e.g., pink) or transparent crystals are also highly rated. Due to the small size of the crystals, micromount specimens are the most common form in collections. ## Popular Localities By far the most sought-after and classic specimens come from the type locality – the Champion Mine in California. Crystals from there, often grown on pyrophyllite or lazulite, are considered exemplary for this species.
Care and storage
## Cleaning Woodhouseite specimens should be cleaned very carefully, using a soft brush to remove dust. If necessary, distilled water can be used, but prolonged soaking should be avoided. Always thoroughly dry the specimen after wet cleaning. ## What to Avoid Woodhouseite is sensitive to acids, which can damage or destroy it. Contact with all household and laboratory chemicals should be avoided. It should also not be heated or subjected to ultrasound in a cleaner. ## Storage It is recommended to store specimens in separate, padded collector boxes to protect them from mechanical damage and scratching by harder minerals. It should be protected from dust and moisture.