Kempite
Chemical formula: Mn²⁺₂Cl(OH)₃
Kempite is a very rare manganese hydroxychloride, forming tiny, emerald-green acicular or bladed crystals.
Properties
- Mohs hardness
- 3.5
- Color
- Emerald-green, brownish-orange
- Luster
- Vitreous
- Streak
- Pale green
- Density
- ~2.94
- Cleavage
- Perfect on {010}
- Fracture
- Uneven
- Transparency
- Translucent
- Crystal system
- Orthorhombic
Diagnostic features
## Identification The key diagnostic feature of kempite is its unique emerald-green color combined with its mode of occurrence – acicular or bladed crystals, often in radial aggregates. Co-occurrence with other manganese minerals, such as pyrochroite and hausmannite, in a specific geological environment is also a strong indicator. ## Distinguishing from Similar Minerals Kempite can be confused with other green, secondary copper or manganese minerals. It is distinguished from malachite by its lack of reaction with hydrochloric acid (malachite effervesces vigorously). Atacamite, chemically closely related, usually has a darker, blackish-green hue and often a different crystal habit. Final confirmation requires advanced analytical methods, such as X-ray diffraction (XRD). ## Crystal Forms Kempite crystallizes in the orthorhombic system, forming elongated, acicular or bladed crystals. They often occur as radial or fibrous aggregates, as well as thin veins in the rock.
Geological environment
## Genesis Kempite is a secondary hydrothermal mineral, formed by the alteration of manganese ore deposits. It forms in veins cutting through metamorphic rocks, such as metamorphosed cherts, in association with primary and secondary manganese minerals. ## Mineral Associations This mineral most commonly co-occurs with pyrochroite (from which it directly forms through oxidation), hausmannite, rhodochrosite, barite, and manganese oxides. ## Localities The most important and classic locality (type locality) for kempite is the manganese mines in the Cedar Flat and Buckeye area of Santa Clara County, California, USA. It is also known from the Fuka mine in Okayama Prefecture, Japan. These are the only confirmed, significant localities for this mineral worldwide.
Rarity
Very rare
For collectors
## Quality Criteria Most valued by collectors are specimens with well-formed, transparent crystals of intense, emerald-green color. Rich acicular aggregates or radial clusters, contrasting with a light matrix, are also highly prized. Due to the small size of the crystals, the quality of a specimen often depends on the aesthetics of the entire miniature or micromount. ## Popular Localities By far the most desirable and historically significant specimens come from the type locality in California, USA. Specimens from the Fuka mine in Japan are also valued, but those from the USA are considered classic.
Care and storage
## Cleaning Kempite specimens should be cleaned with the utmost care, preferably using compressed air to remove dust. Contact with water is not recommended, especially if the mineral is on a sensitive matrix. If necessary, a soft, dry brush can be used. ## What to Avoid Contact with acids and other chemicals that could damage it should be strictly avoided. The mineral is relatively soft and brittle, so it must be protected from impacts and scratches. It should not be heated or subjected to ultrasound. ## Storage Collector specimens of kempite, due to their delicacy and rarity, should be stored in sealed "micromount" boxes, which protect them from dust, moisture, and mechanical damage. Exposure to direct sunlight should be avoided, although there is no evidence of fading.