Rhodochrosite Composition, Crystallization & Structure

Composition Manganese protocarbonate, MnCO₃ = Carbon dioxide 38.3, manganese protoxide 61.7. Iron is usually present, replacing a part of the manganese and sometimes calcium, magnesium, zinc, etc.

Crystallization. Hexagonal-rhombohedral. Crystals unit rhombohedrons (same as cleavage rhombohedron), frequently with curved faces

Structure. Usually cleavable massive; granular to compact. Rarely in crystals.

Physical Properties. Perfect rhombohedral cleavage (cleavage angle = 107°). H. = 3.5-4.5. G. = 3.45-3.6. Vitreous luster. Color usually some shade of rose-red; may be light pink to dark brown. Transparent to translucent.

Tests. Infusible. Soluble in hot hydrochloric acid with effervescence. Gives reddish violet color to borax bead when heated in O. F. Told usually by its pink color, rhombohedral cleavage and hardness (4). Distinguished by its hardness from rhodonite (MnSiO3)(H. = 5.5-6.5).

Occurrence. A comparatively rare mineral, occurring in veins with ores of silver, lead and copper, and with other manganese minerals. Found in the silver mines of Rumania and Saxony. In the United States at Branchville, Connecticut; Franklin, New Jersey; in good crystals at Alicante, Lake Co., at Alma, Park Co., and elsewhere in Colorado.

Name. derived from two Greek words meaning rose and color, in allusion to its rose-pink color.

Use. A minor ore of manganese.