Mineral Information and Data:

CuB(OH)4Cl [CNMNC approved formula]

Named for Mark Chance Bandy (1900-1963), American mining engineer, mineralogist, and mineral collector, who first collected the mineral.

IMA status : Valid species (Pre-IMA 1938) Grandfathered
(8th edition) :  
  (25) Anhydrous Borates Containing Hydroxyl or Halogen
(10th edition) :
  (06) Borates
  (06.A) Monoborates
  (06.AC) B(O,OH)4, without and with additional anions; 1(T), 1(T)+OH, etc
Crystal system: Tetragonal System
Point group (H-M): 4/mmm (or 4/m 2/m 2/m) — ditetragonal-dipyramidal
Unit cell: a = 6.19Å, c = 5.61Å
Crystal Habit: As crystals, typically tabular on {001} or pyramidal, to 5 mm; dominant forms are {001}, {111}, {201}, and {110}; also as radial clusters, almost lichen-like, in joints in the rock.
Color: Deep blue with greenish portions; cendre blue to Italian blue, becoming greener with atacamite inclusions; blue in transmitted light.
Diaphaneity: Transparent
Luster: Vitreous, pearly on cleavage surfaces; dull when altered.
Hardness (Mohs): 2.5
Measured Density: 2.810 g/cm3
Cleavage: {001}, perfect
Tenacity: Very flexible; easily deformed.
Streak: Pale blue
Geologic Setting: Of secondary origin, in a leached zone above massive iron sulfates (Quetena, Chile).
Mineral Association: Atacamite, eriochalcite (Quetena, Chile); starkeyite (near Taltal, Chile)
Other Properties: H2O Soluble.
Comments: Alters to eriochalcite on exposure to air.