Clinohumite
Chemical formula: Mg<sub>9</sub>(SiO<sub>4</sub>)<sub>4</sub>F<sub>2</sub>
Clinohumite is a rare magnesium silicate, prized by collectors for its intensely orange, well-formed crystals.
Properties
- Mohs hardness
- 6
- Luster
- Vitreous to resinous
- Streak
- Yellowish white
- Density
- 3.2-3.4
- Cleavage
- Poor/Indistinct on {001}
- Fracture
- Uneven to Conchoidal
- Transparency
- Transparent to translucent
- Crystal system
- Monoclinic
Diagnostic features
## Identification Clinohumite is most easily identified by its characteristic, intense orange or yellow color, vitreous luster, and occurrence in white, crystalline marble. In well-formed crystals, the typical often flattened shape of the monoclinic system is visible. ## Distinguishing from Similar Minerals Clinohumite can be confused with other minerals from the humite group, such as chondrodite or humite itself. Distinguishing them without advanced studies (e.g., optical or X-ray) is very difficult, and often impossible. It differs from grossular (hessonite) by its lower hardness and different environment of occurrence. Unlike similarly colored sphalerite, clinohumite does not exhibit such perfect cleavage. ## Crystal Forms Clinohumite crystals are usually small and have a complex, often flattened or wedge-shaped structure. It most commonly occurs as irregular grains or small aggregates embedded in the rock. Well-formed crystals are rare and often show numerous, tiny faces.
Geological environment
## Genesis Clinohumite is a metamorphic mineral. It forms as a result of contact metamorphism of carbonate rocks (limestones and dolomites) that have been intruded by hot magma. This process, called skarn formation, requires high temperatures and the presence of volatile components, such as fluorine, which react with the minerals of the host rock. ## Mineral Associations Clinohumite typically co-occurs with minerals characteristic of skarns and metamorphosed marbles. Its most common associates are calcite, dolomite, spinel (especially colorless or blue), forsterite, diopside, phlogopite, graphite, and other minerals from the humite group (chondrodite, humite, norbergite). ## Localities The most important and well-known localities worldwide, from which the best collectible specimens originate, are located in the Pamir Mountains in Tajikistan (Kukh-i-Lal region). Other significant localities include the Taymyr Peninsula in Russia and the historical locality at Vesuvius in Italy. It also occurs in the USA (New York, California) and Canada, but specimens from these places rarely match the quality of those from Tajikistan.
Rarity
Rare
For collectors
## Quality Criteria The most important criterion for evaluating a clinohumite specimen is the intensity and purity of its color – vibrant, orange hues are most desired. Other factors include the crystal's transparency, its size, and the degree of face development. The most highly prized are sharp, undamaged, transparent crystals set on a contrasting, white marble matrix. The presence of associated minerals, such as sparkling spinels, can further enhance the specimen's appeal. ## Popular Localities By far the most valued and sought-after clinohumite specimens by collectors come from the Kukh-i-Lal region in the Tajik Pamir. This is where the largest, best-formed, and most intensely colored crystals originate, serving as the benchmark for this mineral in the collector's market.
Care and storage
## Cleaning Clinohumite specimens, especially those embedded in matrix (e.g., in marble), are best cleaned with a soft, dry brush to remove dust. For heavier soiling, a damp cloth and distilled water can be used, followed by immediate and thorough drying of the specimen. Ultrasonic and steam cleaners should be avoided. ## What to Avoid Clinohumite is sensitive to strong acids, which can damage it. Contact with household chemicals and cleaning agents should be avoided. Although it is quite hard, it should be protected from impacts and contact with harder minerals (e.g., quartz, corundum), which can scratch it. It should not be heated or exposed to sudden temperature changes. ## Storage Clinohumite specimens are best stored in separate boxes or display cases with compartments to prevent scratching from other minerals. Particularly valuable crystals on matrix should be displayed in enclosed cabinets, protecting them from dust and mechanical damage.