The distinctive spinifex texture is formed by skeletal, platy, or acicular crystals of olivine, orthopyroxene, or clinopyroxene, or their pseudomorphs in ultramafic and mafic lavas or silicate-rich furnace slag. In lavas, these crystals form a pattern on weathered surfaces which Australian geologists compared to the local desert grass Triodia spinifex . In Canada, the term is synonymous with “chicken track,” “bird’s foot,” “bird track,” “herring bone,” “feather,” or “lath” textures. The large lath-like or platy crystals, or skeletal, branching or acicular bundles of olivine or pyroxenes are set in a matrix of irresolvable material interpreted as devitrified glass. This groundmass may contain hopper-faced olivine phenocrysts, skeletal, cruciform magnetite and a variety of feathery crystallites.
This komatiite sample displays the characteristic “spinifex texture” defined by extremely acicular olivine phenocrysts–probably a sign of rapid crystallization from a significantly-undercooled magma.