AR'RAGONITE, a mineral essentially consisting of carbonate of lime, and so agreeing in chemical composition with calcareous spar (q.v), but differing from it in the form of its crystals, of which the primary form is a rhombic prism with angles of 116° 16' and 63° 44', the secondary forms being generally prismatic and pyramidal. The effect of heat on them shows another difference, A. being reduced to powder by a heat in which calcareous spar remains unchanged. Such differences between minerals of the same chemical composition appeared very improbable, and when Strorneyer, in 1813, detected the presence of a little carbonate of strontia in A., they were immediately ascribed to this as their cause; but it has since been shown not only that the quantity of strontia is very small, variable, and therefore to be regarded as accidental, but also that the differ ences between the two minerals may be accounted for by difference of temperature when crystallization was taking place. 11. appears to be the product of a crystallization taking
place at a higher temperature than that in which calcareous spar is produced; and accord ingly it is frequent in volcanic districts and in the neighborhood of hot springs, as at Carlsbad. It is frequently found in trap-rocks, as in Scotland. It derives its name from the province of Aragon in Spain. It sometimes occurs stalactitic. Its crystals are some times prisms shortened into tables, sometimes they are lengthened into needles. Twin crystals (mimics) arc very common. Satin spar is a variety of it, in which the crystals are of a fine fibrous silky appearance, anti combined together into a compact mass. Flos ferri (i.e., flower of iron) is a name given to a coralloidal variety which sometimes occurs in iron mines.