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Johachidolite

Class: Borates

In a nepheline dike cutting limestone (North Korea) (Anthony et al., 2001—2005). One of the rarest gemstones.

Original description: Iwase, E., Saito, N., 1942. Johachidolite—A New Mineral of Hydrous Fluoborate of Sodium, Calcium and Aluminium — Scientific Papers of the Institute of Physical and Chemical Research 39: 300—304 [view in ‘Library’]; Aristarain, L. F., Erd, R. C., 1977. Johachidolite redefined: a calcium aluminum borate — American Mineralogist 62: 327—329 [view in ‘Library’].

Type locality: Sangpal-tong [Johachido], North Hamgyong, North Korea.

Type material: unknown; National Museum of Natural History, Smithsonian Institution, Washington, DC, USA, 105479 was used for species redefinition (Anthony et al., 2001—2005).

Etymology: for its type locality, Johachido, an obsolete Japanese name.

Distribution: the mineral is known only from North Hamgyong, North Korea and Mogok, Mandalay, Myanmar.

Chemistry

CaAlB3O7

Essential elements: boron (B), oxygen (O), aluminium (Al), calcium (Ca).

Crystal data

Crystallography: orthorhombic — dipyramidal. Crystal habit: equant subhedral crystals to several millimetres, typically granular (Anthony et al., 2001—2005).

Physical properties

Cleavage: on {201} (Anthony et al., 2001—2005). Fracture: subconchoidal (Anthony et al., 2001—2005). Tenacity: no data. Hardness: 7.5 (Lazzarelli, 2012). Density: 3.45 g/cm3 (Lazzarelli, 2012). Luminescence: blue fluorescence under SW UV, with weak phosphorescence (Anthony et al., 2001—2005).

Optical properties

Colour: colourless, white, pale yellow (Anthony et al., 2001—2005). Diaphaneity: transparent to translucent (Anthony et al., 2001—2005). Lustre: vitreous (Anthony et al., 2001—2005). Refractive index: 1.717—1.724 — anisotropic [biaxial (+)] (Lazzarelli, 2012). Birefringence: 0.007. Dispersion: strong (Anthony et al., 2001—2005). Pleochroism: none.

Material from ‘Repository’

2 specimens: 0174 — 0.03 ct, Myanmar; 0661 — 0.03 ct, Myanmar.


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