large smoky quartz-rock crystal twin crystal with embedded greenish-brown tourmalines

A large smoky quartz-rock crystal twin crystal from Madagascar, with embedded greenish-brownish tourmaline crystals. A three-mineral constellation in a twinned aggregate.

Smoky quartz and rock crystal are quartz varieties with different trace element configurations. Both growing together as twins show the crystallographic sequence of the deposit. The embedded tourmalines (presumably dravite-schorl mixed crystals) are a separate pegmatitic generation.

The greenish-brownish tourmaline coloration is unusual. Standard schorl is black, green verdelite is clear green. A greenish-brown mixed coloration indicates Mg/Cr/Fe trace element mixtures, an intermediate variant of the tourmaline spectrum.

Madagascar supplies such polymineralic quartz specimens from the pegmatite deposits of the Vakinankaratra region. Multi-component aggregates with twinned quartz and tourmaline inclusions are classified as top gemmological specimens in the collector's trade.

A collector's item with complex pegmatitic genesis.