Mixite is one of just a handfull of bismuth minerals and one of even
fewer bismuth arsenates. Other bismuth arsenates include walpurgite
to name a couple. Mixite is probably the best known of these, but is still
a rare mineral by most considerations. It forms in the oxidation zone of
metal ores that probably contained primary bismuth sulfides such as emplectite.
As a mineral collection specimen, mixite is truly a wonderful addition.
It forms nice radial clusters called spherules, made up of fine acicular
crystals. The color is typically a brilliant green of one shade or another
coupled with an attractive silky luster.
Mixite lends its name to a small group of rather obscure
minerals called the
Mixite Group. The
Mixite Group is a group of hexagonal, hydrated copper arsenate and phosphate hydroxides with a general
formula of ACu6(XO4)3(OH)6
- 3H2O The A
in the formula can be either bismuth, aluminum, calcium, cerium, lanthanum,
yttrium, neodymium or thorium. The X
can be either arsenic or phosphorous.
These are the members of the Mixite Group:
(Hydrated Lanthanum Yttrium Calcium Cerium Neodymium Copper Arsenate
(Hydrated Aluminum Yttrium Copper Arsenate Hydroxide)
- Mixite (Hydrated Bismuth Copper Arsenate Hydroxide)
(Hydrated Yttrium Calcium Copper Phosphate Hydroxide)
Agardite actually represents at least a couple of minerals and is sometimes
considered a mineral group itself.
Agardite and mixite are difficult to differentiate.
But if the specimen is associated with other bismuth minerals, than this can prove diagnostic in mixite's favor.
- Color is green, emerald-green, blue-green, yellow-green or off-white.
- Luster is vitreous or silky to dull.
- Transparency: Crystals are transparent to translucent.
- Crystal System is hexagonal.
- Crystal Habits include radiating clusters, tufts or spherules
of acicular or fibrous crystals, also massive, capillary and earthy.
- Cleavage not noticeable.
- Fracture is fibrous.
- Hardness is 3 - 4.
- Specific Gravity is approximately 3.8 - 4.0 (above average for
- Streak is light green.
- Associated Minerals are pharmacosiderite,
- Notable Occurrences include Germany; El Carmen Mine, Durango,
Mexico; France; Jachymov of the former Czechoslovakia; Inyo County, California and Gila and Pinal Counties in
- Best Field Indicators are color, crystal habit, density and
associations with bismuth ores.