Agardite

Formula:  (La, Ca)Cu₆(AsO₄)₃(OH)₆.3H₂O

Origin of name:  for Jules Agard, French geologist, B.R.G.M., Orléans, France

Crystal system:  Hexagonal

Crystal class:  6/m or 6

Twinning:

Unit cell:  a = 13.586 Å, c = 5.931 Å

Colour:  Colourless, blue-green, yellow-green

Diaphaneity: Semitransparent

Luster: Vitreous

Habit:  Crystals acicular in spherical to rosette-like aggregates to 3 mm

Hardness:  3 to 4

Specific gravity: 3.65

Cleavage:

Tenacity:

Streak: Greenish white

Synonyms/varieties:  Chlorotile

Comments:  Two distinct species with the extensions -(La) and -(Y) indicating the predominant rare earth cation in the formula. Nd and Ce have also been noted as dominant rare earth elements, but the corresponding species have not been fully described yet. Member of the mixite group. Found in small amounts in the oxidised zone of hydrothermal mineralised breccia and polymetallic mineral deposits.