. 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. DIAMOND: OCCURRENCE IN SOUTH AFRICA 189. Melaphyre' \ Vertical, or nearly vertical crevices, not more than three-eighths of an inch across and filled with a mineral substance resembling talc in character, penetrate the material down to the lowest dejith to which the mines have been worked. These divide the whole contents of each pipe into a number
. 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. DIAMOND: OCCURRENCE IN SOUTH AFRICA 189. Melaphyre' \ Vertical, or nearly vertical crevices, not more than three-eighths of an inch across and filled with a mineral substance resembling talc in character, penetrate the material down to the lowest dejith to which the mines have been worked. These divide the whole contents of each pipe into a number of vertical or nearly vertical columns, each n. Xeef cgg^^r==^==^.=^wt ~^^=â ^ri:' s. differing slightly from theothers in composition, but showing no difference in its own mass. These small variations in the material filling the pipes, as well as its character as a wholcj^ do not depend in any way upon the nature of the various rocks of the surround- ing reef. It was formerly con- tended that the character of the reef had a more or less marked influence on the richness in diamonds of the material filling the pipes ; thus it was feared that when the base of the black shale in the Kimberley mine had been reached, the yield of diamonds would cease, since the formation of diamonds was supposed to have been de- pendent on some way on the presence of carbon in these shales. In consequence of this belief, the value of mining claims for a time fell; but the yield of diamonds at lower levels, where the pipe is sur- rounded by. melaphyre, turned out to be just as good as at the higher levels in the shale. Between the material fil- ling the "pipes and the enclosing i-ocks or reef there is always a sharp line of demarcation and never a gradual transition. Usually the two sets of rocks are in immediate contact, but not infrequently they are separated by a space, sometimes of considerable width, into which project beautiful crystals of calcite. Other secondary minerals are also found
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