Obsidian is a kind of black glass formed when the heat of a volcano melts the silica material in sand.

VOA: special.2009.09.16

You take a material like silver and put it in a glass case and that's the definition of a meter.

你拿某种材料,比如银,把它放进玻璃柜里,那是一米的定义

耶鲁公开课 - 基础物理课程节选

Scientists said the glass came from material created as deep as three hundred kilometers below the moon's surface.

VOA: special.2009.07.29

Then,she started making statues out of cement material and glass.

VOA: special.2010.04.14