Johachidolite

Chemical formula: CaAlB₃O₇

Johachidolite is a rare, hard, and typically pale yellow borate mineral, valued by collectors for its well-formed crystals.

## Characteristics Johachidolite is a complex calcium and aluminum borate, occurring as transparent to translucent crystals. It typically forms short, prismatic or tabular crystals, often with a pseudohexagonal outline, which can reach several centimeters in size. Its surfaces can be corroded or covered with natural etchings. It is a hard and relatively dense mineral. ## Physical Properties Johachidolite is characterized by its high hardness, measuring 7.5 on the Mohs scale, which makes it resistant to scratching. It has a vitreous luster and is transparent to translucent. Its density ranges from 3.38 to 3.42 g/cm³. It does not exhibit fluorescence under ultraviolet light. ## Colors and Varieties The most common color of johachidolite is pale yellow to yellowish-green. It also occurs in colorless, white, gray, and more rarely, pale green shades. There are no named varieties, and color differences result from minor trace element impurities. ## History and Name The mineral was discovered in 1942 in Johachido (now Sanchon) in Korea. Its name is derived directly from its discovery locality. It was described by Japanese mineralogists Iwamoto and Takechi. ## Applications Due to its rarity and small crystal sizes, johachidolite has no industrial applications. The purest and largest specimens are sometimes faceted and find their way into advanced gemological collections, but they are extremely rare on the market.

Properties

Mohs hardness
7.5
Color
Colorless, white, pale yellow, light green
Luster
vitreous
Streak
White
Density
3.4
Cleavage
none
Fracture
Sub-Conchoidal
Transparency
Transparent
Crystal system
Orthorhombic

Diagnostic features

## Identification Johachidolite can be identified by its characteristic yellow color, high hardness (7.5 on the Mohs scale), and specific, often pseudohexagonal crystal shape. It has a vitreous luster and is relatively heavy for a mineral with a non-metallic appearance. It occurs in a very specific geological environment – syenite pegmatites. ## Distinguishing from Similar Minerals It can be confused with beryl (especially heliodor), danburite, topaz, or phenakite. It differs from beryl by its higher density and orthorhombic crystal system (beryl crystallizes in the hexagonal system). It differs from danburite and topaz in hardness and occurrence environment. Phenakite is harder and crystallizes in the trigonal system. Precise identification often requires advanced studies. ## Crystal Forms Johachidolite crystals are typically short, prismatic, often flattened and tabular. Twinning is common, which gives the crystals a pseudohexagonal appearance. It occurs as single, well-formed crystals or small groups thereof.

Geological environment

## Genesis Johachidolite is a magmatic mineral, crystallizing in the late stages of the formation of nepheline-syenite pegmatites. It forms in an environment rich in boron, aluminum, and calcium, and poor in silica. ## Mineral Associations It most commonly co-occurs with minerals typical of alkaline pegmatites, such as nepheline, albite, microcline, aegirine, eudialyte, lorenzenite, and other rare borates. ## Localities The most important and historical locality, from which the best specimens originate, is Sanchon (formerly Johachido) in South Korea. This mineral has also been found in Myanmar (Burma), in the Mogok region, where it occurs as rounded grains in alluvial deposits. Other confirmed localities include Tajikistan (Leczyorskie Mountains massif in the Pamir) and Russia (Kola Peninsula).

Rarity

Very rare

For collectors

## Quality Criteria The most highly prized johachidolite specimens are those with an intense, pure, yellow color, high transparency, and sharp, well-defined crystal faces. Crystals with a pseudohexagonal outline, free from mechanical damage, are particularly sought after. Size is a key factor – specimens exceeding 1 cm are already considered significant. Internal clarity (lack of inclusions and fractures) increases value, especially for material suitable for faceting. ## Popular Localities Undoubtedly, the most classic and valued specimens come from the original locality in Sanchon, South Korea. Material from Mogok, Myanmar, although often of good gemological quality, primarily occurs as rounded fragments rather than well-formed crystals. Specimens from Tajikistan and Russia are extremely rare on the collector's market.

Care and storage

## Cleaning Johachidolite specimens can be safely cleaned using lukewarm water with a mild soap and a soft brush. After washing, they should be thoroughly rinsed with distilled water and allowed to dry completely. ## What to Avoid The mineral is sensitive to strong acids, so contact with chemicals and aggressive cleaning agents should be avoided. Despite its high hardness, it is brittle and susceptible to mechanical damage upon impact. It should not be subjected to sudden temperature changes or cleaned in ultrasonic cleaners. ## Storage Collector's specimens of johachidolite are best stored in separate, padded boxes to prevent scratching by harder minerals (like diamond or corundum) and damage to more delicate minerals in the collection. It is stable under household conditions and does not require special humidity control or protection from light.

External references

Sources

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