Calcite

CaCO₃

Non-silicate

Crystal system: trigonal (-)

Colour in hand specimen: white
Cleavage: rhombohedral
Hardness: 3

Colour in plane polarised light: colourless 
Pleochroism: none 
Relief: low 
Birefringence:0.172-(0.190); >4^th order 
Extinction: inclined 
Twinning: lamellar, common

M540 Calcite with banded hematite 
Egremont, Cumberland 
Mass of acicular (needle-like) calcite crystals 
Colourless with some grey and red impurities

M541 Calcite 
Iceland spar 
Iskifjördhr, Iceland 
Single crystal of calcite 
Colourless, transparent 
Hardness 3 
Observe the double refraction 
Rhombohedral cleavage (three cleavages)

M542 Calcite vein material 
Minsterley, Shropshire 
Rhombohedral cleavage (three cleavages) 
Pearly lustre 
Hardness 3

L110 Rhyolite, porphyritic (quartz porphyry) 
L130 Andesite, porphyritic (porphyrite) 
L161 Basalt, amygdaloidal
L325 Sandstone, calcareous cement 
L341 Mudstone, calcareous 
L350 Limestone, argillaceous 
L353 Limestone, oolitic, packstone 
L371 Chert, bedded