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Sec. II, Ch. 5: The Brazilian Diamond

Sec. II, Ch. 5: The Brazilian Diamond Page of 366 Sec. II, Ch. 5: The Brazilian Diamond Text size:minus plus Restore normal size   Mail page  Print this page
108
Brazilian Diamonds.
Itacolumite, a rock which was named by Eschwege, from the Serra do Itacolumi. The true Itacolumite of peno­logists is a sandstone, remarkable for possessing flexibility, so that a thin slab admits of being readily bent to and fro. This pecular rock is, however, only a rare variety of the Itacolumite, most of which is a granular schistose quartzite, or metamorphic sandstone, destitute of flexibility.
The Brazilian Itacolumite long figured in works on mineralogy as the original matrix—the true parent-rock .—of the Diamond ; and the occurrence of a somewhat similar rock with Diamonds in India and in North Carolina led to premature generalizations as to the origin of the gem.
In the geological section under description, the Itaco-lumites are associated with a group of hydro-mica schists and Itaberites, or schists containing specular iron-ore. Traversing these rocks are certain more or less defined veins of clayey matter containing Diamonds. The mineral is here supposed to occur in its primitive position, the clayey material being probably its decaying matrix. Dia­monds are also found in the quartzites of an overlying series, but here they are to be regarded as pebbles washed out of their original home in the lower group of rocks. They are likewise distributed through the gravels of the Brazilian Highlands, where they find a resting-place after having been set free from their enclosing matrix. It is possible then that a Diamond, born originally in the lower metamorphic series, may have been transported among the materials which enter into the constitution of the upper series, and then on the wearing down of these upper rocks, may have been once more disturbed, and finally deposited in the gravels of the present river valleys. Such appears to be the geological history of many a Brazilian Diamond.
Sec. II, Ch. 5: The Brazilian Diamond Page of 366 Sec. II, Ch. 5: The Brazilian Diamond
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