Humite
Chemical formula: Mg<sub>7</sub>(SiO<sub>4</sub>)<sub>3</sub>F<sub>2</sub>
Humite is a rare magnesium silicate from the humite group, prized by collectors for its honey-yellow to orange-brown, well-formed crystals.
Properties
- Mohs hardness
- 6
- Luster
- Vitreous to resinous
- Streak
- White to yellowish
- Density
- 3.14-3.33
- Cleavage
- Poor on {001}
- Fracture
- Uneven to subconchoidal
- Transparency
- Transparent to translucent
- Crystal system
- Orthorhombic
Diagnostic features
## Identification Humite is primarily identified by its characteristic honey-yellow to orange-brown color, vitreous luster, and occurrence in specific geological environments – contact metamorphic rocks such as skarns and marbles. Hardness (6 on the Mohs scale) and relatively high density are also helpful indicators. Under shortwave UV light, some specimens may exhibit yellow or orange fluorescence. ## Distinguishing from Similar Minerals Humite is difficult to distinguish from other minerals within its own group, especially clinohumite and chondrodite, without advanced studies (e.g., optical or X-ray). Clinohumite crystallizes in the monoclinic system (humite in the orthorhombic) and more often forms larger, better-developed crystals. Chondrodite can be very similar but often has a slightly lighter, more yellow hue. It is distinguished from olivine by its common presence in marbles and skarns, whereas olivine is typical of igneous rocks (mafic and ultramafic). ## Crystal Forms Humite crystals are rare and usually small. They take the form of short prisms, often with modified and rounded faces, giving them a barrel-like appearance. Most often, it occurs as embedded, rounded grains or granular aggregates within the host rock (marble).
Geological environment
## Genesis Humite is a mineral typical of contact metamorphism processes. It forms as a result of the interaction of fluorine-rich hydrothermal solutions with carbonate rocks (limestones and dolomites) in contact zones with magmatic intrusions. This process, called metasomatism, leads to the formation of skarns and marbles, in which humite crystallizes. ## Mineral Associations This mineral often co-occurs with other minerals typical of skarns and metamorphosed carbonate rocks. Its most common associates include: calcite, dolomite, spinel, brucite, phlogopite, diopside, vesuvianite, grossular (garnet), and other minerals from the humite group (clinohumite, chondrodite, norbergite). ## Localities The historical and type locality for humite is the Somma-Vesuvius volcanic complex in Campania, Italy, where it occurs in volcanic ejecta. Other well-known occurrences include mines in the Franklin region of New Jersey (USA), deposits in Pargas, Finland, on the Kola Peninsula in Russia, and in the Badakhshan region of Afghanistan and the Pamir Mountains in Tajikistan, from which gem-quality material originates.
Rarity
Rare
For collectors
## Quality Criteria The most highly prized humite specimens are those with sharp, well-formed, and transparent crystals of intense orange or reddish-brown color. Aesthetic contrast with a white rock matrix, most often marble, is of great importance. Specimens with multiple crystals or in attractive groups are more desirable than single grains. Clarity (lack of inclusions and fractures) and strong luster also significantly increase collector value. ## Popular Localities Although Vesuvius is historically the most important locality, the most highly valued specimens by collectors come from newer discoveries. Localities in Afghanistan (Badakhshan) and Tajikistan (Pamir) provide the world's best gem-quality humite and clinohumite crystals. Classic, though usually smaller, specimens also come from Franklin, USA, and Finland.
Care and storage
## Cleaning Humite specimens should be cleaned very carefully, using a soft brush to remove dust. For heavier soiling, lukewarm distilled water and a mild detergent can be used, followed by thorough rinsing and immediate drying with a soft cloth. Ultrasonic cleaners and steam cleaners should be avoided. ## What to Avoid Humite is sensitive to strong acids, especially sulfuric acid. Contact with household and laboratory chemicals should be avoided. It should not be subjected to rapid temperature changes, which can cause internal fractures. Prolonged exposure to intense sunlight is not recommended, although there is no evidence of fading. ## Storage Collector's humite specimens, especially those with fragile crystals, are best stored in separate, padded boxes to prevent scratches and mechanical damage. They should be protected from dust and moisture. Specimens on a rock matrix are generally more stable but still require careful handling.