Volltext Seite (XML)
FOLIATED GRANULAR LIMESTONE. 1H Geognostic Situation. This mineral occurs in beds, in granite, gneiss, mica- slate, clay-slate, syenite, greenstone, grey-wacke, and rarely in some of the floetz rocks. It is observed, that the varieties which occur in the older rocks are in general more highly crystalline than those which are found in the newer. It frequently contains imbedded minerals of different kinds, such as quartz, mica, hornblende, tremo- lite, sahlite, asbestus, steatite, serpentine, galena, blepde, iron-pyrites, and magnetic’ironstone: of these the quartz and mica are the most frequent. Geographic Situation. This mineral occurs in all the great ranges of primi tive and transition rocks that occur in Lurope, and in such a6 have been examined in Asia, Atrica, and Ame rica. It is observed, that in general the white and grey varieties abound in primitive countries; the variegated in those composed of transition rocks. All ol them re ceive a good polish, and hence are known to artists as •marbles. Uses. All the varieties of this subspecies may be burnt into •luicklime; but it is found, that in many of them, the concretions exfoliate and separate during the volatiliza tion of their carbonic acid, so that by the time w hen they are rendered perfectly caustic, their cohesion is destroyed, and they fall into a kind of sand,—a circumstance which " ill always render it improper to use such varieties in a common kiln. Hut the most important use of this mi neral is as marble. The marbles we ore now to men tion,
