THE MINERAL SAINFELDITE

Chemistry: Ca5(AsO4)2(AsO3{OH})2 - 4H2O, Hydrated Calcium Arsenate Hydroxide.
Class: Phosphates
Subclass: Arsenates
Uses: Only as mineral specimens.
Specimens

Sainfeldite is a rare mineral but is becoming a popular collection mineral. It forms nice rosette clusters of crystals with an attractive pink color. Although the crystals are usually small, they do provide a good sparkle and make for good specimens.

Sainfeldite's chemistry is unusual in that it has the unusual ion group of AsO3{OH}. This group is the same as the regular arsenate ion group except that one of the four oxygens is replaced by an hydroxide or OH group. Sometimes the formula for sainfeldite is written as Ca5H2(AsO4)4 - 4H2O. Other arsenates with this chemical oddity include pharmacolite, guerinite and picropharmacolite, all of which are associated with sainfeldite. The mineral hureaulite is similar, but with a phosphate as the affected ion group.

PHYSICAL CHARACTERISTICS:

Color is mostly a pale pink, white or colorless.
Luster is vitreous.
Transparency: Crystals are transparent to translucent.
Crystal System is monoclinic; 2/m
Crystal Habits include small prismatic crystals with slanted pinacoidal faces sometimes in radiating clusters or rosettes.
Cleavage is absent.
Fracture is uneven
Hardness is 4
Specific Gravity is approximately 3.0 (slightly above average for translucent minerals).
Streak is white.
Associated Minerals are pharmacolite, guerinite, picropharmacolite and other secondary arsenates.
Notable Occurrences include Richelsdorf, Germany and Ste. Marie-aux-Mines, Alsace, France.
Best Field Indicators are color, locality, associations and crystal habit.