THE MINERAL KUPLETSKITE

Chemistry: (K, Na)3(Mn, Fe)7(Ti, Nb)2(SiO3)8(O, OH)7, Potassium Sodium Manganese Iron Titanium Niobium Silicate Hydroxide.
Class: Silicates
Subclass: Inosilicates
Group: Astrophyllite
Uses: Only as mineral specimens.
Specimens

Kupletskite is a very rare manganese, titanium mineral found in some unusual rock assemblages called agpaitic pegmatites. It forms two solid solution series with the minerals astrophyllite and cesium-kupletskite. A solid solution series is where two or more minerals share the same structure, but vary their chemistry by specific limits. In these cases, astrophyllite and kupletskite vary in the amount of manganese and iron. Kupletskite is the manganese rich end member of the series and astrophyllite is the iron rich end member. Except for the minor change in chemistry, their structures are the same.

The mineral astrophyllite is the namesake of the mineral group to which all three minerals, kupletskite, astrophyllite and cesium-kupletskite belong; the Astrophyllite Group of minerals. The solid solution series between kupletskite and cesium-kupletskite involves the enrichment of the series with the element cesium in the potassium/sodium site of the structure. Cesium-kupletskite's formula is thus written as Cs3(Mn, Fe)7(Ti, Nb)2(SiO3)8(O, OH)7.

PHYSICAL CHARACTERISTICS:

Color is bronze yellow or dark brown to black.
Luster is vitreous or submetallic to metallic, can be pearly on cleavage surfaces.
Transparency: crystals are translucent to opaque.
Crystal System is triclinic; bar 1
Crystal Habits include small tabular, acicular or bladed crystals. Also found in lamellar, micaceous or fibrous masses.
Cleavage is perfect in one direction, poor in another.
Fracture is uneven.
Hardness is 3.
Specific Gravity is 3.2 - 3.4
Streak is pale brown.
Associated Minerals are quartz, nepheline, microcline, albite, calcite, natrolite, fluorite, eudialyte, ancylite, arfvedsonite, micas and aegirine.
Notable Occurrences include the Kola Peninsula, Russia and Mt St. Hilaire, Quebec, Canada.
Best Field Indicators: brittleness, cleavage, color, luster and localities.