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Mg3B7O13Cl A white, yellow, green, or blue orthorhombic borate mineral occurring in crystals which appear isometric in external form; it is strongly pyroelectric, has a hardness of 7 on Mohs scale, and a specific gravity of 2.9.



a mineral from the group of anhydrous borates. Chemical composition Mg3[B7O12]OCl. It contains 62.5 percent B2O3. It crystallizes into a rhombic (pseudocubic) sys-tem. The structure is of the complex shell type and contains [BO3]3- and (BO4)5-. Part of the Mg may be replaced by Fe2+. Boracite forms shiny crystals of cubic, tetrahedral, or dodecahedral appearance. The color is bluish-gray; frequently, it is colorless. Its hardness on the mineralogical scale is 7.5; its density is 2,930–2,950 kg /m3. Boracite is rare. It is formed in sedimentary deposits of gypsum, anhydrite, and potassium and rock salts.

References in periodicals archive ?
However, a series of larger nodules up to about 1 meter in diameter, found at or near the base of the Boulby Potash in the north and west of the mine, have furnished most of the line boracite specimens collected in the 1990s.
This is not a distinct mineral species; analyses showed its composition to be borderline between boracite and trembathite.
At the Boulby mine, boracite occurs within massive sylvinite ore in a variety of habits ranging from isolated single crystals to large nodules.
Examination of the boracite nodules suggests that some are formed by aggregation of spherules a few millimeters in diameter.
It is the type locality for povondraite and magnesioriebeckite, and has also produced abundant sharply-formed, doubly-terminated danburite crystals, the world's largest boracite crystals, and interesting specimens of ericaite, dolomite, magnesite, and several other species.
The mine has recently been reported in mineralogical journals as a new locality for well-crystallized boracite and hilgardite (Robinson and King, 1993; Cooper, 1994; Moore, 1994; Weiss, 1994).
Most of the unusual species described below, including anhydrite, boracite, ericaite, hilgardite, magnesite, rectorite and syngenite were identified by X-ray powder diffraction at Manchester University.
Anhydrite occurs very rarely within boracite nodules as poorly developed, pale lilac, translucent, equant to prismatic crystals.
This is not a distinct mineral species; analyses show its composition to be borderline between boracite and ericaite.
The Boulby mine, Loftus, Cleaveland, Yorkshire, has continued to produce more of the remarkable pale blue-green boracite crystals.
He introduced powdered boracite into the blowpipe flame and it showed a typical green color.
A boracite update from England: the Boulby potash mine near Cleveland in Yorkshire is still operating (barely) and the general quality of these lovely pale green sparkling boracite druses is up from the time of the last Denver Show.