Polished Komatiite slab KOM118

Komatiite is a rare type of ancient volcanic rock formed from exceptionally hot, magnesium-rich lava. Most komatiites formed billions of years ago when the Earth’s interior was much hotter than it is today. The lava was extremely fluid and could flow rapidly over considerable distances, often across the ancient seafloor. As it cooled, minerals such as olivine and pyroxene crystallised from the lava. Some komatiites developed the distinctive spinifex texture, made up of long, blade-like crystals arranged in striking sprays and patterns.

As the lava cooled, long blade-like crystals grew rapidly through the molten rock, producing distinctive sprays and criss-crossing patterns resembling the leaves of spinifex grass.
Because the lava was so hot and fluid, it initially contained very few crystals.
As the top of the lava flow cooled rapidly, crystals—particularly olivine and pyroxene—started growing downward into the still-hot liquid lava beneath. Rather than forming ordinary chunky crystals, they grew extremely quickly as long, thin plates or blades.
The crystals competed for space as they grew. Some developed in roughly parallel groups, while others formed beautiful fans, sprays and intersecting patterns. Eventually the remaining lava cooled and solidified around them, permanently preserving the pattern.
From the famous Norseman-Wiluna Greenstone Belt—one of the world's most significant and widely studied Archean volcanic terranes.