Diamonds and precious stones, a popular account of gems .. . Figs. 69 and 70.—Modified Crystals of Quartz. the other, oxygen, is a gas, and one of the principalconstituents of atmospheric air. The primitive form of quartz is the rhombohedron,but the primitive crystals are extremely rare. Themost common form is the regular hexagonal prismterminated with six-sided pyramids (Fig. 6è). It is rare for the terminal pyramids to have allthe faces equal. Ordinarily, on the contrary, threeof these faces are developed at the expense of the ISO PRECIOUS STONES. other three, and thus we have the crystal re
Diamonds and precious stones, a popular account of gems .. . Figs. 69 and 70.—Modified Crystals of Quartz. the other, oxygen, is a gas, and one of the principalconstituents of atmospheric air. The primitive form of quartz is the rhombohedron,but the primitive crystals are extremely rare. Themost common form is the regular hexagonal prismterminated with six-sided pyramids (Fig. 6è). It is rare for the terminal pyramids to have allthe faces equal. Ordinarily, on the contrary, threeof these faces are developed at the expense of the ISO PRECIOUS STONES. other three, and thus we have the crystal repre-sented by Fig. 69. In other cases the crystals are not terminated bypyramids, but by ridges, as in Fig. 70. In thiscase the form of the crystals is greatly altered, andthe regularity, to a certain extent, disappears. If in the regular crystal (Fig. 68) we suppose theprismatic part to be diminished little by little with-out the form being otherwise changed, then, when
Size: 1464px × 1707px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1870, booksubjectgems, booksubjectprec
