Browse Items (264 total)

Compare with phenocryst.

Formula Fe3O4 Structure Non-silicate Crystal System Crystal system: cubic Physical Properties Colour in hand specimen: blackStreak: blackCleavage: noneHardness: 7.5-8 Optical Properties Colour in plane polarised light: almost…

Have a look at pyrite (M520) in the 1A Reference Series.

Formula K2(Mg,Fe2+)6-4(Fe3+,Al,Ti)0-2[Si6-5Al2-3O20](OH,F)4 Structure Sheet silicate Crystal System Crystal system: monoclinic (-) Physical Properties Colour in hand specimen: brown or black Cleavage: one, good Hardness: 2-3 Optical…

Formula K2Al4[Si6Al2O20](OH,F)4 Structure Sheet silicate Crystal System Crystal system: monoclinic (-) Physical Properties Colour in hand specimen: colourless Cleavage: one, good Hardness: 2.5-3 Optical Properties Colour in plane…

Have a look at muscovite mica (M301, M302) and biotite mica (M303, M304) in the 1A Reference Series.

See cross-hatched twins.