Journal - South African Institute of Mining and Metallurgy . ocking, thus creating difficulty inpreparing the slide as they easily separated duringgrinding. This accounted for the comparativebrittleness of these pebbles, as the difference insizes of grains may account for uneven Xo. II., on the other hand, an importedpebble, the structure is crypto-crystalline andhomogeneous, and in places distinctly is probably composed therefore of the Chalce-donic variety of silica, , a true flint, and nodifficulty was met with in making the greater brittleness and sli
Journal - South African Institute of Mining and Metallurgy . ocking, thus creating difficulty inpreparing the slide as they easily separated duringgrinding. This accounted for the comparativebrittleness of these pebbles, as the difference insizes of grains may account for uneven Xo. II., on the other hand, an importedpebble, the structure is crypto-crystalline andhomogeneous, and in places distinctly is probably composed therefore of the Chalce-donic variety of silica, , a true flint, and nodifficulty was met with in making the greater brittleness and slightly inferior hard-ness of the local pebbles, of course, influencestheir wearing qualities, the imported pebbles last-ing longer, though the difference, I believe, is notvery considerable and may be offset by the lowercost. It is, however, obvious, that consideringonly the local pebbles, the more the quartz grainsinterlock the less easily will they be separatedand the less brittle will the pebble be. In somequartzites this interlocking is very marked, and. I [G. 11. IMPORTED PEBBLE 1 the rock is in consequence comparatively Iand strong, and it would seem, therefore, thatthe microscope may furnish valuable inform Ias to the suitability of proposed pebbles, andalso liners, for employment in tube nulls. With regard to liners, Mr. Weber has kindlyfurnished me with the appended note embodyingsome of his observations, and, in conclusion, Imay perhaps offer an opinion, that in tube millpebbles and liners the important properties arethree in number ; hardni ind homo- geneity, the order of importance in the case ofpebbles being as given, and in the case of liner>,hardness, homogeneity and tough- Hardness is a sine ?, homogeneity results in even wear, of great importance withliners ; while pebbles particularly require tough-ness to resist breaking when tumbling about inthe mill. The imported pebbles and linersapparently excel in each of these qualil Liners (by M. Weber),—During the
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