Takedaite is a

borate mineral The Borate Minerals are minerals which contain a borate anion group. The borate (BO3) units may be polymerised similar to the SiO4 unit of the silicate mineral class. This results in B2O5, B3O6, B2O4 anions as well as more complex structures whic ...

that was found in a mine in Fuka,

Okayama Prefecture is a Prefectures of Japan, prefecture of Japan located in the Chūgoku region of Honshu. Okayama Prefecture has a population of 1,826,059 (1 February 2025) and has a geographic area of 7,114 Square kilometre, km2 (2,746 sq mi). Okayama Prefecture ...

Japan Japan is an island country in East Asia. Located in the Pacific Ocean off the northeast coast of the Asia, Asian mainland, it is bordered on the west by the Sea of Japan and extends from the Sea of Okhotsk in the north to the East China Sea ...

during a mineralogical survey in the year 1994. During the survey, Kusachi and Henmi reported the occurrence of an unidentified anhydrous borate mineral closely associated with nifontovite, olshanskyite, and

calcite Calcite is a Carbonate minerals, carbonate mineral and the most stable Polymorphism (materials science), polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on ...

. By the year 1994 two other minerals in the borate group M₃B₂O₆ had been identified in nature Mg₃B₂O₆ known as kotoite and Mn₃B₂O₆ known as jimboite. Takedaite has the ideal chemical formula of Ca₃ B₂ O₆. The mineral has been approved by the Commission on New Minerals and Mineral Names, IMA, to be named takedaite after Hiroshi Takeda, a professor at the Mineralogical Institute, University of Tokyo Japan.

Occurrence

Takedaite is found in association with

gehlenite Gehlenite, (Ca2Al lSiO7, is a sorosilicate, Al-rich endmember of the melilite complete solid solution series with akermanite.Deer et al., 1993 The type locality is in the Monzoni Mountains, Fassa Valley in Trentino in Italy, and is named after ...

spurrite Spurrite is a white, yellow or light blue mineral with monoclinic crystals. Its chemical formula is Ca5( Si O4)2 CO3. Spurrite is generally formed in contact metamorphism zones as mafic magmas are intruded into carbonate rocks.Smith, J.V. (196 ...

, bicchulite, rankinite, kilchoanite, oyelite, and fukalite. It occurs in a vein consisting of

borate A borate is any of a range of boron oxyanions, anions containing boron and oxygen, such as orthoborate , metaborate , or tetraborate ; or any salt of such anions, such as sodium metaborate, and borax . The name also refers to esters of su ...

minerals that developed along the boundary between crystalline

limestone Limestone is a type of carbonate rock, carbonate sedimentary rock which is the main source of the material Lime (material), lime. It is composed mostly of the minerals calcite and aragonite, which are different Polymorphism (materials science) ...

and the skarns. The vein it was discovered in was approximately 10 cm in thickness and is closely associated with frolovite and calcite. At the circumference of the expanded area, hydrous borates such as nifontovite, olshanskyite, sibirskite, and pentahydroborite occurred 20 cm to 50 cm in thickness.

Physical properties

Takedaite is a white, or pale gray mineral with a

vitreous luster Lustre (Commonwealth English) or luster (American English; see spelling differences) is the way light interacts with the surface of a crystal, rock, or mineral. The word traces its origins back to the Latin ''lux'', meaning "light", and generall ...

and colorless in thin sections. It exhibits a hardness of 4.5 on the

Mohs hardness scale The Mohs scale ( ) of mineral hardness is a qualitative ordinal scale, from 1 to 10, characterizing scratch resistance of minerals through the ability of harder material to scratch softer material. The scale was introduced in 1812 by the Germ ...

. The density measured by heavy liquids was 3.10(2) g•cm⁻³, the calculated density being 3.11 g•cm⁻³.

Optical properties

Takedaite is optically uniaxial Negative. The refractive indices are: ω = 1.726, ε = 1.630, and the Vickers microhardness was 478(429-503) kg mm⁻² (25g load). The

infrared spectrum Infrared (IR; sometimes called infrared light) is electromagnetic radiation (EMR) with wavelengths longer than that of visible light but shorter than microwaves. The infrared spectral band begins with the waves that are just longer than those of ...

of Takedaite measured by the KBr method for the region 4000 to 250 cm⁻¹. The absorption bands at 907, 795, 710, and 618 cm⁻¹ were in close agreement with those of the synthetic 3CaO·B₂O₃ reported by Wier and Schroeder (1964). The absorption bands at 1275 and 1230 cm⁻¹ for takedaite were sharper.

Chemical properties

Takedaite is a

with the presence of

calcium Calcium is a chemical element; it has symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar to it ...

boron Boron is a chemical element; it has symbol B and atomic number 5. In its crystalline form it is a brittle, dark, lustrous metalloid; in its amorphous form it is a brown powder. As the lightest element of the boron group it has three ...

and

oxygen Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...

. Chemical analysis gave CaO 71.13%, B₂O₃ 28.41%, the H₂O content was determined by ignition loss at 900 °C and was 0.14%, totaling 99.68%. The empirical formula calculated on the basis of O=6 is therefore Ca_3.053B_1.965O₆ or more ideally Ca₃B₂O₆. Takedaite is also easily soluble in dilute

hydrochloric acid Hydrochloric acid, also known as muriatic acid or spirits of salt, is an aqueous solution of hydrogen chloride (HCl). It is a colorless solution with a distinctive pungency, pungent smell. It is classified as a acid strength, strong acid. It is ...

Chemical composition

X-ray crystallography

The x-ray powder data for takedaite was obtained by an X-ray diffractometer using Ni-filtered Cu-Κα radiation. Single crystals were also studied using the precession and Weissenberg methods. Takedaite is in the

trigonal In crystallography, the hexagonal crystal family is one of the six crystal family, crystal families, which includes two crystal systems (hexagonal and trigonal) and two lattice systems (hexagonal and rhombohedral). While commonly confused, the tr ...

crystal system. The

space group In mathematics, physics and chemistry, a space group is the symmetry group of a repeating pattern in space, usually in three dimensions. The elements of a space group (its symmetry operations) are the rigid transformations of the pattern that ...

is either Rc or R3c. The

unit cell In geometry, biology, mineralogy and solid state physics, a unit cell is a repeating unit formed by the vectors spanning the points of a lattice. Despite its suggestive name, the unit cell (unlike a unit vector In mathematics, a unit vector i ...

dimensions, refined by least squares from the X-ray powder diffraction data of takedaite, were: a = 8.638(1) Å, c = 11.850(2) Å.

References

{{reflist Natural materials Borate minerals Calcium minerals Trigonal minerals Minerals described in 1994 Wikipedia Student Program