Borate minerals

name colour lustre Mohs hardness specific gravity

boracite colourless or white vitreous 7–7½ 2.9–3.0

borax colourless to white; grayish, bluish, greenish vitreous to resinous 2–2½ 1.7

colemanite colourless; white, yellowish, gray brilliant vitreous to adamantine 4½ 2.4

inyoite colourless, becoming white and cloudy after partial dehydration vitreous 2 1.7

kernite colourless vitreous 2½ 1.9

ludwigite dark green to coal black silky 5 3.6 (lud) to 4.7 (paig)

priceite white earthy 3–3½ 2.4

sussexite white to straw-yellow silky to dull or earthy 3–3½ 2.6 (szai) to 3.3 (suss)

tincalconite white (natural); colourless (artificial) vitreous 1.9

ulexite colourless; white vitreous; silky or satiny 2½ 2.0

name habit or form fracture or cleavage refractive indices crystal system

boracite isolated, embedded, cubelike crystals conchoidal to uneven fracture alpha = 1.658–1.662

beta = 1.662–1.667

gamma = 1.668–1.673 orthorhombic (isometric above 265 degrees C)

borax short prismatic crystals one perfect, one good cleavage alpha = 1.445

beta = 1.469

gamma = 1.472 monoclinic

colemanite short prismatic crystals; massive one perfect, one distinct cleavage alpha = 1.586

beta = 1.592

gamma = 1.614 monoclinic

inyoite short prisms and coarse crystal aggregates; geodes; drusy crusts; granular massive one good cleavage alpha = 1.492–1.495

beta = 1.501–1.510

gamma = 1.516–1.520 monoclinic

kernite very large crystals; fibrous, cleavable, irregular masses two perfect cleavages alpha = 1.454

beta = 1.472

gamma = 1.488 monoclinic

ludwigite fibrous masses; rosettes; sheaflike aggregates no observed cleavage alpha = 1.83–1.85

beta = 1.83–1.85

gamma = 1.97–2.02 orthorhombic

priceite soft and chalky to hard and tough nodules earthy to conchoidal alpha = 1.569–1.576

beta = 1.588–1.594

gamma = 1.590–1.597 triclinic(?)

sussexite fibrous or felted masses or veinlets; nodules alpha = 1.575–1.670

beta = 1.646–1.728

gamma = 1.650–1.732 probably orthorhombic

tincalconite found in nature as a fine-grained powder; physical properties are given for artificial pseudocubic crystals hackly fracture omega = 1.461

epsilon = 1.474 hexagonal

ulexite small nodular, rounded, or lenslike crystal aggregates; fibrous botryoidal crusts; rarely as single crystals one perfect, one good cleavage alpha = 1.491–1.496

beta = 1.504–1.506

gamma = 1.519–1.520 triclinic