The density of the
globules (2.58) is similar to that of ordinary varieties of calcite. It
is probable that if the operation were to take place under the influence
of heat, under the conditions above mentioned, aragonite would be
formed. It is hardly necessary to dwell upon the possible geological
applications of this mode of forming calcareous oolites and pisolites.
ON CRYSTALS OF ANHYDROUS LIME.
Some time ago it was discovered that some limestone, which had been
submitted for eighteen months to a heat of nearly 1,000 degrees in
the smelting furnaces of Leroy-Descloges (France), had given rise to
perfectly crystallized anhydrous lime. Figure C shows three of these
crystals magnified 300 diameters. It will be noticed that they have a
striking analogy with grains of common salt. They are, in fact, cubes
(often imperfect), but do not polarize light, as a substance of the
first crystalline system should. However, it is rarely the case that the
crystals do not have _some_ action on light. Most usually, when the two
Nicol prisms are crossed so as to cause extinction, the crystals present
the appearance shown at D. That is to say, while the central portion
is totally inactive there are seen on the margins zones which greatly
brighten the light.
[Illustration]
A and B.--Calcareous Pisolites and Oolites produced artificially.
A.--External aspect and section of a Pisolite.
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