Vivianite, Fe2+3(PO4)2 .8H2O is a hydrated iron phosphate mineral. The specimen is composed of radiating dark stellate crystals of vivianite with a hint of dark blue, which are mounted on a rock which also has botryoidal manganese oxides. The specimen is from the Kerch iron-ore basin, Eastern Crimea, Ukraine.
Stauralite, Fe2+2Al9O6(SiO4)4(O,OH)2 is a regional metamorphic neosilicate mineral. It is classed as an index mineral,and is useful in determining the depth, pressure, and temperature at which metamorphism occurs. This specimen displays the characteristic "Stauralite cross". The cross is the result of cruciform penetration twinning of the stauralite crystals..The specimen is from the Kola peninsula, Russia.
Calcite, CaO3, Calcium carbonate. Calcite can be so varied in appearance that inevitabely it features very commonly in most collections, and my collection is no exception. This specimen is composed of scalenahedral crystals on an iron rich base. The crystals have a minor coating of an orange colour, probably iron staining. Collected a very long time ago when I should have known better, it's origin is unknown.
This is a pretty little specimen of Calcite CaO3 and galena PbS both of which are common hydrothermal minerals. The Calcite crystals are scalenahedral and well formed, but the galena which has grown between the calcite crystals, is very poorly formed. The specimen, which is only of interest because of it's visual appeal is from the Madan ore field in Bulgaria.