Calcite and Aragonite on Dolostone

Sample of grey/brown acicular Aragonite and large subhedral rhombohedron colourless Calcite crystal embedded in Dolostone. Aragonite crystals have a vitreous lustre and Calcite crystal has a dull lustre. Average Aragonite crystal: 0.2 cm x 0.2 cm 0.05 cm. Calcite crystal size: 2.6 cm x 1.5 cm x 0.6 cm. Calcite (CaCO3) can be white, colourless or pale shades of grey, yellow, red, green, blue or brown and black when impure. Lustre is vitreous or dull and streak is white. Hardness is 3 and cleavage is perfect in three directions forming a rhombohedron. Calcite usually occurs as rhombohedron, scalenohedron or prisms but can also be tabular, acicular, cleavable, granular, compact, stalactitic, oolitic or earthy. Aragonite (CaCO3) can be white, grey, colourless, yellow, pale green, violet or brown. Lustre is vitreous or resinous and streak is white. Hardness is 3 1/2 to 4 and cleavage is good in one direction and poor in two other directions. Aragonite usually occurs as long to short prismatic crystals but can also be fibrous acicular, columnar or stalactitic aggregates.