A popular treatise on gems, in reference to their scientific value; a guide for the teacher of natural sciences, the jeweller, and amateur: together with a description of the elements of mineralogy, and all ornamental and architectural materials .. (1859)
Feuchtwanger, Lewis. [from old catalog] · New York, D. Appleton & company · leaf 44
rare. Open forms.—Tetragonal prisms (fig. 30) bounded byfour planes parallel to the principal axis; ditetragonalprisms by eight similar planes. In these prisms the. prin-cipal axis is supposed to be prolonged infinitely, or to beunbounded. Where it is very short and the lateral axes FORM OF… … Fi&29. Fig. 80. determine these, one of the series must be chosen as thefundamental form, and for this purpose a tetragonal pyramidof the first variety, designated by P as its sign, is selected.The angle of one of its edges, especially the middle edge,found by measurement, determines its…
Precious stones · Building stones · Mineralogy
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