Kurnakovite

Kurnakovite is a hydrated borate of magnesium with the chemical composition MgB₃O₃(OH)₅·5H₂O. It is a member of the inderite group and is a triclinic dimorph of the monoclinic inderite.^[3]

Kurnakovite
Kurnakovite from Boron, California
General
Category	Nesoborates
Formula	MgB3O3(OH)5·5H2O
IMA symbol	Kko[1]
Strunz classification	6.CA.20
Crystal system	Triclinic
Crystal class	Pinacoidal (1) (same H-M symbol)
Space group	P1
Unit cell	a = 8.3479(1) b = 10.6068(1) c = 6.4447(1) [Å] α = 98.846°, β = 108.981° γ = 105.581°; Z = 2
Identification
Color	White; colorless in transmitted light
Crystal habit	Aggregates of prismatic crystals
Twinning	Twinning uncommon
Cleavage	Poor to indistinct on {010}
Mohs scale hardness	2+1⁄2 – 3
Luster	Vitreous
Streak	White
Diaphaneity	Transparent to translucent
Specific gravity	1.847 – 1.852
Optical properties	Biaxial (-)
Refractive index	nα = 1.488 – 1.491 nβ = 1.508 – 1.510 nγ = 1.515 – 1.525
Birefringence	δ = 0.027 – 0.034
2V angle	Measured: 60° to 80°
References	[2][3][4]

Discovery and occurrence

Kurnakovite, was first described by Godlevsky in 1940 for an occurrence in the Inder lake borate deposits in Atyrau Province, Kazakhstan, and is named for Russian mineralogist and chemist Nikolai Semenovich Kurnakov (1860–1941).^[2]

In addition to the type locality in Kazakhstan, kurakovite has also been reported from the Zhacang-Caka brine lake, Tibet; the Kirka borate deposit, Kiitahya Province, Turkey; the Kramer borate deposit, Boron, Kern County, California; Death Valley National Park, Inyo County, California; and the Tincalayu borax deposit, Salar del Hombre Muerto, Salta Province, Argentina.^[2][3]

Properties

Kurnakovite has triclinic – pinacodial crystallography. It forms as rough, prismatic crystals, typically in dense aggregates. Kurnakovite has distinct cleavage and a conchoidal fracture. Its tenacity is brittle and it ranges between 2.5 – 3 on the Mohs hardness scale. It is not soluble in water, though it will start dissolving in warm acid. Kurnakovite is usually colorless or white and either transparent or translucent. It has a vitreous, pearly luster and a refractive index of between 1.488 – 1.525.^[2][3][4]