LIMESTONE FAMILY. acuminations of the prism, because it originates from it. The varieties are the following O 1. Flat double three-sided pyramid, often aggregated in rows, or in the pyramidal form. When the py ramids are aggregated in a straight direction, there is formed a six-sided prism, flatly acuminated with three planes, which are ^et in an unconformable position on the lateral edges. 2. The same pyramid, deeply truncated on the apices. From this originates the six-sided table, in which the terminal planes are set alternately oblicpie on the lateral planes. 3. The double three-sided pyramid sometimes be comes rather acute, and approaches to the cube; generally the two angles on the extremities of the axis of the double pyramid are truncated. 4. Very acute double three-sided pyramid: when the two apices of the double pyramid are so deeply trun cated that the truncating planes meet the higher angles of the common basis, an octahedron is form ed. •5. The acute single and double three-sided pyramid, with convex faces. These sometimes exhibit di vided planes, and give rise to the six-sided pyramid of the first division. It would extend this description too much, were we to attempt to give an account of every variety of form ex hibited by these crystals; and besides, we have already enumerated the principal ones. The crystals occur ot various magnitudes, as large, small, and very small. Externally it alternates from splendent to glimmering: internally it alternates from smooth and specular-splen dent to shining. The
