Calcareous spar

Nicol, W. On a method of so far increasing the divergency of the two rays in calcareous spar that only one image may be seen at a time. Edinburgh New Phil. 6, 83-84 (1829). 

The oxide, or lime, occurs in great abundance in,nature chiefly as carbonate, in the forms of marble, limestone, chalk and calcareous spar also as sulphate, in the shape of gypsum and alabaster. Carbonate of lime is the chief ingredient of shells, and phosphate of lime is the earthy part of bones. Lime is found in the ashes of many plants. 

Carbonate of lime occurs native, as marble, limestone, chalk, and calcareous spar. It also forms the chief part of shells, and is often found in springs, dissolved by an excess of carbonic acid. When such water, which is very hard water is boiled, the excess of carbonic acid escapes, the carbonate of lime is deposited, and the water becomes, pro tanto, softer. Or, the same effect may be produced by adding just as much lime-water as will neutralise the bicarbonate of lime, when the whole is precipitated as neutral carbonate. CaO, 2 CO, + Ca O = 2 (Ca 0, CO,). 

Stone within the Head of the Great One s Decade [ ] = realgar Icy Stone = calcareous spar... 

Accurate comparison of results requires knowledge of reaction site density per unit surface area. Calcite materials used for kinetic study have included natural marbles, limestones, hydro-thermal crystals of Iceland spar, tests of calcareous organisms and laboratory and commercial precipitates. Surface areas, estimated by BET methods and graphical methods (based on particle size distribution) range from about 0.005 to 2 m g . There are apparent discrepancies between graphical and BET surface areas and the question is raised as to which type of surface area estimate is most representative of the reacting surface area. 

Calcium Carbonate—CaCO,—100—the most abundant of the natural compounds of Ca, exists as limestone, calcar, cheU , marble, Ice land spar, and arragonite and forms the basis of corals, shells of Crustacea and of molluscs, etc. 

IV. Earths, which by fusion with fixt alkalies form glasses (absorbent, calcareous, magnesia, of alum, crystalline, argillaceous, heavy spar, talk, asbestes, serpentine stone, shirl, zeolites c.). 

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