History, Mining, and Value Chain of Diamonds Practice Test 2026 - Free Practice Questions and Study Guide

These rocks come from cooling and crystallization of molten material that originated inside the Earth. Kimberlite and lamproite form as mantle melts that ascend rapidly and crystallize as they reach shallower depths, often erupting as pipe-like features. That origin from a melt is the defining trait of igneous rocks. Their mineral content reflects mantle-derived melts and their association with diamonds is due to their deep, high-pressure source, not because they are sedimentary or metamorphic. They aren’t formed by deposition of sediments (like clastic rocks) or by metamorphic recrystallization without melting, so they fit squarely into the igneous category.