Abstract

In 1966 crystals of hydrochlorborite were found in the Salar Carcote, Antofagasta Province, Chile. This is the second reported occurrence of the mineral.

Hydrochlorborite is monoclinic, 2/m; space group I2/a or Ia; a=22.783, b=8.745, c= 17.066 Å, β=96.42°; a:b:c =2.605:1:1.952; unit cell volume 3376.9Å3; Z=4; cell content 3CaO·CaCl2·4B2O3·22H2O. Well-formed, colorless crystals with a maximum length of 13 mm show the forms: {001}, {110}, {013}, {112}, {112}, {211}, {211}. The strongest lines in the X-ray powder photograph are in Å: 8.474(100), 6.005(24), 3.605(9), 2.798(8), 2.825(7).

Hydrochlorborite is optically (+); α = 1.499, β= 1.502, γ=1.521 (Na light); 2V=45°; r<υY=b; Z∧c=25°. Good {001} cleavage. Hardness 2½. Specific gravity 1.852 (meas), 1.876 (calc).

Hydrochlorborite appears to be a seasonal mineral. Near-surface crystals formed during the dry season are dissolved with rising water table during the wet season.

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