Lava flow sources Tachylite

flaked stone artefacts australia, made of tachylite

a second mode of occurrence of tachylite in form of lava flows. basaltic rocks contain small amount of glassy ground-mass, , in limburgites becomes more important , conspicuous, vitreous types far less common in these in acid lavas. in hawaiian islands, however, volcanoes have poured out vast floods of black basalt, containing feldspar, augite, olivine, , iron ores in black glassy base. highly liquid when discharged, , rapid cooling ensues on emergence air prevents crystallization taking place completely. many of them spongy or vesicular, , upper surfaces exceedingly rough , jagged, while @ other times assume rounded wave-like forms on solidification. great caves found crust has solidified , liquid interior has subsequently flowed away, , stalactites , stalagmites of black tachylite adorn roofs , floors. on section these growths show central cavity enclosed walls of dark brown glass in skeletons , microliths of augite, olivine , feldspar lie imbedded. crater of mt. kilauea, thin clouds of steam rise constantly, , bubbles of vapor liberated molten rock carry air them thin fibers of basalt solidify @ once , assume form of tachylite threads. under microscope prove glassy small circular air vesicles drawn out long tubes. in hawaiian islands glassy basaltic lavas of kind @ common. small outcrop @ spring hill in victoria, australia has tachylite has been exploited material making aboriginal flaked stone implements.