Browse Items (264 total)

Hand Specimen This rock is made up of light grey sub-spherical ooids. Fine to medium sand grain size. A few lithic/biogenic fragments. Dark grey cement. Small hair-line white veins run through this rock. Thin-section Ooids made up of a greenish…

Hand Specimen This rock is made up of cryptocrystalline silica (quartz), black to brown. Being made up of silica, it is hard and displays conchoidal fracture. This is a flint nodule, which comes from a chalk bed – notice the thin shell of white…

Hand Specimen Two rock types, with an irregular contact between them. 1 – Very dark brown, microcrystalline rock. This fizzes with acid. It is a limestone. 2 – Grey and black, intermingled, microcrystalline silica. Brittle and well jointed. Some…

Hand Specimen Very fine-grained rock with a prominent, well-developed cleavage. The dark red-purple colour is due to iron-staining. The light green smudge is a reduction spot. Thin-section Mud size grains.Mainly indistinguishable clay…

Hand Specimen Strongly developed planar fabric made up of platy biotite mica and muscovite mica grains and lenses of quartz grains. Fabric wraps around large, euhedral garnets, typically ~2mm across. Quartz, the most soluble mineral, has…

Hand Specimen Almost entirely made up of fine sand sized quartz grains. Does not fizz with acid, so no carbonate present. Clean white rock, apart from pink-brown weathering. Dark carbonaceous marks are plant roots. Thin-section Subangular…

Hand Specimen Buff coloured rock.Almost pure quartz, which has been very well recrystallised.Faint banding could be original bedding. Thin-section Fine to medium grained recrystallised quartz with sutured contacts. Rock History The sutured…

Formula (Mg,Fe)2[SiO4] Structure Orthosilicate Crystal System Crystal system: orthorhombic (+) (-) Physical Properties Colour in hand specimen: pale greenCleavage: none, instead it has characteristic curving cracksHardness: 7 Optical…

Formula Zr[SiO4] Structure Orthosilicate Crystal System Crystal system: tetragonal (+) Physical Properties Colour in hand specimen: reddish brown, yellow, grey, green or colourlessHardness: 7.5 Optical Properties Colour in…

Formula CaTi[SiO4](O, OH, F) Structure Orthosilicate Crystal System Crystal system: monoclinic (+) Physical Properties Colour in hand specimen: colourless, yellow, green, brown or blackCleavage: one, goodHardness: 5 Optical…