. Precious stones, a popular account of their characters, occurrence and applications, with an introduction to their determination, for mineralogists, lapidaries, jewellers, etc. With an appendix on pearls and coral. Precious stones; Pearls; Corals. CLEAVAGE S7. Fig. 8. Cleavage of calcite. The direction within a crystal, along which there is minimum cohesion, is known as the direction of cleavage, and the plane surface of separation is known as the cleavage face. The cleavage directions and faces are always identical both in number and direction in all specimens of the same mineral species. T
. Precious stones, a popular account of their characters, occurrence and applications, with an introduction to their determination, for mineralogists, lapidaries, jewellers, etc. With an appendix on pearls and coral. Precious stones; Pearls; Corals. CLEAVAGE S7. Fig. 8. Cleavage of calcite. The direction within a crystal, along which there is minimum cohesion, is known as the direction of cleavage, and the plane surface of separation is known as the cleavage face. The cleavage directions and faces are always identical both in number and direction in all specimens of the same mineral species. The ease with which cleavage takes place, and the perfection of the resulting cleavage faces, are also constant in all specimens of the same species, but different in different species. Some minerals exhibit little or no cleavage, while in others, notably calcite, cleavage is produced very easily, and the surfaces of separa- tion are perfectly bright, smooth, and even. Among precious stones possessing the property of cleavage to a high degree may be mentioned topaz, which cleaves in one direction, and diamond which cleaves in four directions. In others, as, for example, emerald, cleavage takes place with difficulty, and the cleavage faces are uneven and frequently interrupted by irregular areas. Quartz, garnet, tourmaline, &c., are other examples of pi-ecious stones possessing no distinct cleavage ; the difference of cohesion in different directions being so small that the stones will not split along plane surfaces. In amorphous bodies, as, for instance, opal, the degree of cohesion between the constituent particles, like all other physical characters, is identical in every direction, so that here plane cleavage faces are impossible, and as a fact never occur. When a body shows sure indications that it possesses the property of cleavage, we are safe in inferring from that fact alone that the material of which the body is composed is crystallised and not amorphous. Hence it i
Size: 1484px × 1684px
Photo credit: © Central Historic Books / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1900, booksubjectpreciousstones, booky
