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Itacolumite, it-a-kol′ūm-īt, n. a schistose quartzite, containing scales of mica, talc, and chlorite, often having a certain flexibility.

Along beside, and traversing through and through these golden rocks and sands, occur immense bands of itacolumite, known, from its flexibility, as the elastic sandstone.

The diamond, which consists of pure carbon, is generally met with in alluvial deposits, but sometimes, also, in a curious flexible sandstone, called itacolumite.

At Sāo Jo�o da Chapada, in Minas Geraes, diamonds occur in a clay interstratified with the itacolumite, and are accompanied by sharp crystals of rutile and haematite in the neighbourhood of decomposed quartz veins which intersect the itacolumite.

The mountains consist here of an ancient laminated micaceous quartzite, which is in parts a flexible sandstone known as itacolumite, and in parts a conglomerate; it is interbedded with clay-slate, mica-schist, hornblende-schist and haematite-schist, and intersected by veins of quartz.