CALX carbonata (calcite) from British mineralogy by James Sowerby 1802-1817

BGS Image ID: P704769

  CALX carbonata; var. inversa. Inverse crystallized Carbonate of Lime. Plate no. 143

From: Sowerby, James. 1802-1817. British Mineralogy: Or Coloured figures intended to elucidate the mineralogy of Great Britain. Plate from vol: 2. page no.81.

BGS Image ID: P704911

CALX carbonata. Crystallised Carbonate of Lime. Plate no. 285

From: Sowerby, James. 1802-1817. British Mineralogy: Or Coloured figures intended to elucidate the mineralogy of Great Britain. Plate from vol: 3. page no.171. Modern name: Calcite. Location: Samples from the Dimple mine near Matlock.

BGS Image ID: P704940

CALX carbonata, var. metastatica. Metastatic crystallised Carbonate of Lime. Plate no. 314

From: Sowerby, James. 1802-1817. British Mineralogy: Or Coloured figures intended to elucidate the mineralogy of Great Britain. Plate from vol: 4. page no.19. Modern name: Calcite. Location: Sample collected in Derbyshire.

Crushed samples of feldspar from Scotland

BGS image ID:  P527656

Crushed samples of feldspar from Scotland 

Potash feldspar was first in demand for the production of fertilizers, later during the Second World War deposits of potash feldspar were investigated for the production of ceramic ware. British Geological Survey Petrology Collection sample number MC 7436. To extract the potash numerous methods have been devised. They include 1. Simple wet grinding and electrolysis, this proved unsuccessful and only one-third of the alkali present could be extracted by this method. 2. Treatment with chemical solutions, either caustic alkalis or acids. 3. Volatization of potash-salts, this involved heating feldspar with gypsum and carbon with potassium sulphate being volatilized and then recovered. 4. A number of dry processes for the separation of potash existed e.g. separation of potash as hydroxide or carbonate; as sodium or potassium chlorides; extraction of sodium and potassium sulphate.

Bob McIntosh

Garnets from the BGS collections

BGS image ID: P704670

SILEX granatus. Garnet. Plate no. 44. From: Sowerby, James. 1802-1817. British Mineralogy: Or Coloured figures intended to elucidate the mineralogy of Great Britain. Plate from vol: 1. page no.92. Modern name: Garnet.

BGS image ID: P521247

Rock specimen of garnet pegmatite. Loch Garve, Garve, Rosshire, Scotland. The photograph is a detail of the surface of a garnet pegmatite sample, characterized by ruby-red spherical garnets of varying sizes, within a matrix of pale quartz and white mica. British Geological Survey Petrology Collection sample number EMC589. Garnets of this colour are generally rich in iron and manganese, termed 'almandine' garnets. The pegmatites in the Garve area have been dated using radiometric dating techniques, which indicate they are Precambrian in age.

BGS image ID: P524411

Photomicrograph of garnet-mica schist. Light: XPL, Magnification x 2. Glen Roy half a mile north-east of Stone and east of Beinn a' Monicag, Invernessshire. The image is a photomicrograph taken under crossed-polarizing lenses of a thin section of garnet mica-schist. British Geological Survey Petrology Collection sample number S 82420. Light: XPL, Magnification x 2. Light: XPL, Magnification x 2. The sample comes from the Monadhliath Mountains of the Grampian Highlands of Scotland. It is a semipelitic rock (a metamorphosed siltstone or impure sandstone) of Precambrian age which has become completely recrystallized with the development of an assemblage of metamorphic minerals. As the original sedimentary rocks become deeply buried in the Earth's crust they undergo a series of profound changes which, under the effects of elevated temperature and pressure, result in the breakdown of the original sedimentary minerals and the growth of new metamorphic minerals. This specimen is from the Leven Schist Formation, Appin Group, Dalradian Supergroup (Precambrian) from Glen Roy, half a mile north-east of Stone and east of Beinn a' Monicag. This formation consists of laminated, pale grey, pelitic schists which are locally flaggy and variably garnetiferous with thin carbonate beds towards the top of the formation. Following the progressive shallowing associated with the Grampian Group basin there was slow subsidence resulting in a marine transgression which led to the deposition of the Lochaber Subgroup. This was followed by a significant increase in water depth which led to the deposition of the Leven Schist Formation.

Bob McIntosh