Clinohedrite

Chemical formula: CaZn²⁺SiO₄·H₂O

Clinoclase is a rare zinc and calcium silicate, distinguished by its intense, orange fluorescence under ultraviolet light.

## Characteristics Clinoclase is a hydrated zinc and calcium silicate, typically forming small, tabular or wedge-shaped crystals. It occurs as small aggregates, coatings, or as individual, disseminated crystals in rock fissures. Its most characteristic feature, which attracts collectors, is its very strong and distinctive fluorescence under ultraviolet light. ## Physical Properties Clinoclase crystals are relatively soft, with a hardness of 5.5 on the Mohs scale. They have a vitreous luster, and a greasy or resinous luster on fracture surfaces. They are transparent to translucent. The mineral's density is approximately 3.28-3.33 g/cm³. ## Colors and Varieties It is usually colorless, white, pale pink, or light violet. Some specimens may exhibit subtle pleochroism. No distinct color varieties or commercial varieties are recognized. ## History and Name The mineral was first described in 1898 by Samuel L. Penfield and H.W. Foote from samples found at the Franklin Mine in New Jersey, USA. Its name comes from the Greek words *klino* (κλίνω) - "to incline" and *hedra* (ἕδρα) - "face", referring to the wedge-shaped habit of its crystals. ## Uses Clinoclase has no industrial applications. It is valued solely as a collector's mineral, particularly for its exceptional fluorescent properties.

Properties

Mohs hardness: 5.5
Color: Colorless, pale amethystine (rare)
Luster: Vitreous, Resinous
Streak: White
Density: 3.28
Cleavage: On {010}
Fracture: Uneven
Transparency: Transparent,Translucent
Crystal system: Monoclinic

Diagnostic features

## Identification The most important diagnostic feature of clinoclase is its intense, orange to yellow-orange fluorescence under shortwave UV light. In daylight, it can be recognized by its characteristic wedge-shaped crystals and its association with other minerals from the Franklin deposit. ## Distinguishing from Similar Minerals It can be confused with other colorless or white minerals from the Franklin deposit, such as willemite or calcite. However, none of these exhibit such characteristic orange fluorescence. Willemite fluoresces green, and calcite typically fluoresces red or pink. ## Crystal Forms Crystals are usually small, tabular, often with truncated edges giving them a wedge-shaped appearance. They form granular aggregates, radial aggregates, or grow in druses in rock fissures.

Geological environment

## Genesis Clinoclase is a metamorphic mineral. It forms as a result of contact metamorphism of mineralized carbonate rocks, under specific geochemical conditions found in zinc deposits, such as the Franklin deposit in New Jersey. ## Mineral Associations It most commonly co-occurs with franklinite, willemite, zincite, hardystonite, calcite, bustamite, and rhodochrosite. This is a classic association for the Franklin deposit. ## Localities The most important and historical locality for clinoclase is the Franklin Mine in Sussex County, New Jersey, USA, which is its type locality. It is also known from the nearby Sterling Hill Mine. Outside the USA, its presence has been noted at the Christmas Mine in Arizona, and in a few localities in Japan and Namibia, but specimens from there are extremely rare and of no collector significance.

Rarity

Rare

For collectors

## Quality Criteria The most highly prized clinoclase specimens are those with well-formed, sharp, and transparent crystals, set on a contrasting matrix, e.g., with dark franklinite. The intensity and uniformity of the orange fluorescence are key factors. Crystal size is also important – specimens with crystals exceeding a few millimeters are already considered exceptional. ## Popular Localities The vast majority, if not all, collector specimens come from a single location in the world: the Franklin Mine in New Jersey, USA. This is the classic and most sought-after locality for this mineral.

Care and storage

## Cleaning Clinoclase specimens should be cleaned very carefully, using a soft brush to remove dust. If necessary, compressed air can be used. Due to its fragility and potential reactivity, washing with water, especially with detergents, should be avoided. ## What to Avoid Avoid contact with acids and other chemicals that may damage the crystal surfaces. The mineral is brittle, so protect it from impacts and scratches. Do not heat it or subject it to sudden temperature changes. ## Storage Clinoclase specimens are best stored in separate, padded boxes or display cases to avoid contact with harder minerals. Due to its rarity and collector's value, it is recommended to minimize direct exposure to strong light, although it is not particularly susceptible to fading.