Henmilite
Chemical formula: Ca₂Cu[B(OH)₄]₂(OH)₄
Henmilite is a rare copper calcium borate mineral, characterized by an intense blue-violet color and low hardness.
Description
## Characteristics Henmilite is a rare borate mineral that forms small, often acicular or tabular crystals. It usually occurs in radial or fibrous aggregates, and less frequently as single, well-formed crystals. Its most characteristic feature is an intense blue-violet color, which can range from light blue to deep violet. Crystals are typically small, reaching millimeters in length. ## Physical Properties This mineral is characterized by low hardness, which makes it delicate and easily scratched. It has a vitreous luster, and its transparency varies from transparent to translucent. The density of henmilite is approximately 2.51 g/cm³. ## Colors and Varieties The dominant color of henmilite is blue-violet, which is a result of the presence of copper in its chemical composition. Shades may vary depending on the specific specimen and its formation conditions, from light blue to dark violet. No formally recognized varieties of henmilite are known. ## History and Name Henmilite was discovered in 1981. The mineral's name comes from the surnames of two Japanese mineralogists: Henmi Kichinosuke and Henmi Chiyoko, who played a significant role in its identification and research. This discovery took place in the Fuka mine in Japan, which is also the type locality for many other rare borate minerals. ## Uses Due to its rarity, low hardness, and small crystal sizes, henmilite has no industrial applications. It is a mineral of purely collectible and scientific significance, valued for its aesthetics and unique chemical composition.
Diagnostic features
## Identification Henmilite can be identified by its characteristic blue-violet color, low hardness (can be scratched with a fingernail), and vitreous luster. It often occurs as small, acicular or tabular crystals forming radial aggregates. The streak of the mineral is very pale violet to almost white. ## Differentiation from Similar Minerals Due to its color, henmilite can be confused with other blue minerals, such as azurite or dioptase. However, azurite has significantly higher hardness and a different crystallization habit, and dioptase is characterized by a more intense, emerald-green color and higher hardness. The low hardness of henmilite is a key feature distinguishing it from many visually similar minerals. ## Crystal Forms Henmilite typically forms small, acicular or tabular crystals. They often occur as radial or fibrous aggregates. Well-formed, single crystals, which are triclinic, are less common.
Geological environment
## Genesis Henmilite is a secondary mineral that forms under hydrothermal conditions, usually in the oxidation zones of borate deposits. Its presence is often associated with metasomatic carbonate rocks, where reactions occur between solutions rich in boron, copper, and calcium. It occurs in fractures and cavities in marbles and skarns. ## Mineral Associations Henmilite often co-occurs with other borate minerals, such as szaibelyite, kotoite, ludwigite, as well as with calcite, brucite, hydrotalcite, and other copper minerals. This association is typical for environments rich in boron and calcium. ## Localities The most important and type locality for henmilite is the Fuka mine in Okayama Prefecture, Japan. This is also the only known occurrence of this mineral, which emphasizes its rarity.
Rarity
Extremely Rare
Collector aspects
## Quality Criteria The most prized henmilite specimens are those that exhibit an intense, uniform blue-violet color. Crystallization is also important – well-formed, distinct crystals, especially those forming aesthetic radial aggregates, are more sought after. Specimen size matters, although henmilite rarely occurs in large forms. Purity and absence of mechanical damage also affect collectible value. ## Popular Localities The only known and popular locality for henmilite is the Fuka mine in Japan. All prized specimens originate from this location.
Care and storage
## Cleaning Henmilite is a delicate mineral and therefore requires careful cleaning. It is best to use a soft brush or paintbrush to remove dust. For heavier soiling, the specimen can be gently rinsed with lukewarm distilled water, avoiding a strong stream and prolonged soaking. After washing, it should be dried with a soft cloth or left to air dry. ## What to Avoid Avoid using any chemical cleaning agents, including detergents and acids, as they can damage the mineral's surface or alter its color. Henmilite is sensitive to high temperatures and direct sunlight, which can cause color fading. Due to its low hardness, it should be protected from scratches and impacts. Also avoid excessive moisture, which can promote mineral degradation. ## Storage Henmilite specimens should be stored in a dry, cool place, away from direct sunlight and heat sources. It is best to place them in closed display cases or boxes with soft padding to prevent dust accumulation and mechanical damage. Individual packaging of each specimen, for example in soft tissue paper or cotton, will further protect it from scratches.