S

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Flint.

Flint.

Flint, sometimes referred to as chert by geologists, is a cryptocrystalline form of quartz,  SiO2  Very often it is found in chalk deposits as nodules. These specimens which I collected from Sandringham warren in Norfolk interested me because of their non-nodular appearance. The one in particular seems to be a cemented collection of small irregular shaped pieces of flint. The location is from a footpath cutting through a small area of higher ground which exits the warren. Pieces of flint are eroding from the narrow cutting through which the footpath has been cut.

Chalcedony, erratic.

Chalcedony, erratic.

Chalcedony. is a microcrystalline form of silica,  SiO2.  The silica is in two forms, quartz, and moganite, both of which have the same formula, but different crystal structures. The specimen, known as banded chalcedony,  is composed of alternating layers of grey and cream deposits of chalcedony, topped with an encrustation of small quartz crystals.  The crystals are somewhat battered, because this specimen is an erratic that has been transported by an ice sheet. The location is only known as the Lincolnshire fells.

Epidote.

Epidote.

Epidote is  a calcium aluminium iron sorosilicate  mineral, with the formula  Ca2Al2(Fe3+;Al)(SiO4)(Si2O7)O(OH). It is a rock forming mineral of secondary origin, occurring in marble and schistose rocks of metamorphic origin. It may also occur as a product of the alteration of the usual minerals found in igneous rocks, for instance, micas, amphiboles, feldspars, pyroxenes.  The randomly orientated crystals in this specimen are prismatic, and are very dark green, almost black in colour. It was collected from Mount Painter, in South Australia, by the club co-founder Jim Nicholls, while working at Woomera.

Brochantite,  Australia.

Brochantite, Australia.

Brochantite is a sulphate mineral, Cu4SO4(OH)6, often referred to as a secondary mineral of copper. The encrustation on this specimen is a mix of brochantite and another copper secondary mineral, probably malachite in the form of minute botryoidal clusters ( see insets).  The brochantite crystals are prismatic, and very small, scattered here and there throughout the specimen, and are a very slightly darker green.  This Australian specimen was collected in the 1960's by our club co-founder, Jim Nicholls, while he was working there on rocket technology.