Book digitized by Google from the library of Harvard University and uploaded to the Internet Archive by user tpb.
Includes bibliographical references and index
Purchase of this book includes free trial access to www.million-books.com where you can read more than a million books for free. This is an OCR edition with typos. Excerpt from book: MINERALS OF ECONOMIC VALUE, LOCALITIES OTHER THAN NEW SOUTH WALES. These show-cases should be studied from left to right. GEMSTONES. Case 78 South Africa.In the first column on the left are diamonds Diamond. and models, the largest of the latter representing a stone weighing 103- carats. 5962, a stone weighing 1'4 carats, represents one of the most characteristic forms assumed by diamonds crystalsan eight- sided double pyramid (octahedron). 2343, a not uncommon flattened form of tetrahedron (3 carats). 5961, a very remarkable specimen (3| carats), consistingof three cubes intergrown. It is rare to find the diamond crystallising in the form of the cube. The edges of the cube are modified by a series of overlapping faces of the octahedron, giving rise to an appearance of bevelling such as would result from the presence of the rhombic dodecahedron. The stone is grey in tint, measuring 5 mm. in length of edge, and weighing 3-j carats. 2345, carbonado. 2316, a most interesting specimen, showing a small crystal embedded in the so-called "blue ground" in which the Kimberley stones are found. The crystal has the usual pyramid shape: the striations on the faces should be noticed.t The nature of the country, and of the material in which the diamonds are found, is well shown by a good series of specimens, and by descriptive labels and diagrams at the head of the showcase. The stones are found scattered through a decomposed material occupying oval pipes vertically traversing the basalts, shales, and quartzites of the country. This material is known as " blue ground." As the diamond-bearing material is now crushed immediately on coming from the mine, tis very unlikely that specimens such as this will be forthcoming in the future, t For remarks about diamo...