Kotoit

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Kotoit
Kotoite, Ludwigite, Szaibélyite-140414.jpg
Massive, coarsely crystalline aggregate of kotoite (light gray), ludwigite (black, fibrous) and szaibélyite (whitish, earthy weathering crust on the right) from the "Nalednoe B" deposit, Tas-Khayakhtakh mountain range, Sacha , eastern Siberia (size: 6.5 × 4.5 × 2.5 cm)
General and classification
chemical formula Mg 3 [BO 3 ] 2
Mineral class
(and possibly department) 		Borates (formerly carbonates, nitrates and borates)
System no. to Strunz
and to Dana 		6.AA.35 ( 8th edition : V / G.01)
03/24/02/01
Crystallographic Data
Crystal system orthorhombic
Crystal class ; symbol orthorhombic-dipyramidal; 2 / m  2 / m  2 / m
Space group Pnmn (No. 58, position 5)Template: room group / 58.5
Lattice parameters a  = 5.40  Å ; b  = 8.42 Å; c  = 4.50 Å
Formula units Z  = 2
Twinning polysynthetic twins according to {101}
Physical Properties
Mohs hardness 6.5
Density (g / cm 3 ) measured: 3.10; calculated: 3.09
Cleavage completely after {110}; Secretions after {101}
Break ; Tenacity not defined
colour colorless, white
Line color White
transparency transparent
shine Glass gloss
Crystal optics
Refractive indices n α  = 1.652
n β  = 1.653
n γ  = 1.673
Birefringence δ = 0.021
Optical character biaxial positive
Axis angle 2V = 21 ° (measured); 26 ° (calculated)
Other properties
Chemical behavior Easily soluble in warm hydrochloric and sulfuric acid

Kotoite is a rarely occurring mineral from the mineral class of " borates " (formerly carbonates, nitrates and borates) with the chemical composition Mg 3 [BO 3 ] 2 . From a chemical point of view, it is therefore a magnesium borate that structurally belongs to the island borates.

Kotoite crystallizes in the orthorhombic crystal system , but has so far only been found in the form of granular to massive mineral aggregates . It is colorless and transparent, but can also appear white due to multiple refraction due to polycrystalline formation.

Etymology and history

Kotoit was first discovered in the gold-copper-bismuth mine "Hol Kol" in the North Korean province of Hwanghae-pukto, belonging to the district of Suan-gun, and described in 1939 by Takeo Watanabe , who named the mineral after Bundjirô Kotô (1856-1935), who worked as a geologist and petrograph at the University of Tokyo and studied the ore deposits of Hol Kol in North Korea.

Watanabe carried out the necessary work for the analysis and description of the mineral in the Mineralogical-Petrographic Institute of the University of Berlin, actively supported by the well-known mineralogist and then director Paul Ramdohr .

classification

In the meanwhile outdated, but still in use 8th edition of the mineral classification according to Strunz , the kotoite belonged to the common mineral class of " carbonates , nitrates and borates" and to the department of "island borates", where it was named after the "kotoite group" with the system No. V / G.01 and the other members Jimboit and Takedait .

The 9th edition of Strunz's mineral systematics , which has been in effect since 2001 and is used by the International Mineralogical Association (IMA), assigns kotoite to the newly defined mineral class of "borates" and there in the department of "monoborates". This is further subdivided according to the possible presence of additional anions in the formula and the structural arrangement of the borate complex. The simply built kotoite is accordingly in the subsection “BO 3 without additional anions; 1 (Δ) ”, which means that the BO 3 triangles are connected in approximately hexagonal layers. Together with Jimboit he also forms the "Kotoitgruppe" with the system no. 6.AA.35 .

In the Dana system of minerals used in the English-speaking world , the carbonates, nitrates and borates form a common mineral class as in the outdated Strunz system. There the kotoite is in the department of “anhydrous borates” and the subdivision “ anhydrous borates with (A) m (B) n [XO 3 ] p ”, where it also forms the unnamed group 03/24/02 together with Jimboit .

Crystal structure

Kotoite crystallizes orthorhombically in the space group Pnmn (space group no. 58, position 5) with the lattice parameters a  = 5.40  Å ; b  = 8.42 Å; and c  = 4.50 Å and 2 formula units per unit cell . Template: room group / 58.5

Education and Locations

Kotoite forms primarily or secondarily as a secondary component through contact metasomatosis (rock transformation through material displacement ) in magnesium-rich skarn- borate deposits and in metamorphosed dolomitic marble . The accompanying minerals include fluoborite , forsterite , clinohumite , ludwigite , spinel , suanite , szaibélyite and warwickite .

As a rare mineral formation, Kotoite could only be detected at a few sites, whereby so far (status: 2013) almost 20 sites are known. At its type locality , the gold-copper-bismuth mine "Get Kol" and so far the only known locality in North Korea, the mineral, however, occurred in a large amount (at the time of the discovery estimated over 1000 tons) in the northern, eastern and western ore bodies revealed .

Other well-known sites include Lianping and Changning in China, Miyako (Iwate) on the Japanese island of Honshū, Băița (Bihor) in Romania, the "Titovskoe" deposit in the Tas-Khayakhtakh mountain range of the East Siberian Republic of Sakha (Yakutia) and the Jumbo Mountain in Darrington ( Snohomish County ) in the State of Washington.

See also

literature

Web links

Commons : Kotoite  - collection of images, videos and audio files

Individual evidence

  1. ↑ a b c d e Hugo Strunz , Ernest H. Nickel: Strunz Mineralogical Tables . 9th edition. E. Schweizerbart'sche Verlagbuchhandlung (Nägele and Obermiller), Stuttgart 2001, ISBN 3-510-65188-X , p.  329 .
  2. ↑ Webmineral - Kotoite
  3. ↑ a b c Kotoite. In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America. 2001. ( PDF 65.1 kB )
  4. ↑ a b c d e Mindat - Kotoite
  5. ↑ Mindat - Number of localities for Kotoit
  6. ↑ Takeo Watanabe: Kotoite, a new rock-forming magnesium borate. 1939.
  7. ↑ Find location list for Kotoite at the Mineralienatlas and at Mindat