Crystal

Acryl, colloquially referred to as crystal.
Crystal is a material with near-identical mechanical properties to polymethyl methacrylate. Brittle, though with some give, and harder to scratch than most wood. Far less dense than stone. It is often found at higher elevations, such as in mountains.
The material has a very low melting point (160c), and is often molded into shapes.
Crystal is dimensionally neutral.
(actually an amorphous solid like glass and not a crystal in the chemical sense)