Silicates & Quartz
Tectosilicate
What it is
Framework silicates where every oxygen is shared between tetrahedra, creating a rigid 3D network. This includes feldspars, zeolites, and the rare hackmanite, which changes color in sunlight.
How it forms
Forms in igneous and metamorphic rocks. Hackmanite's remarkable tenebrescence (reversible color change in UV light) comes from sulfur atoms trapped in the framework.
Fully linked SiO₄ / AlO₄ framework
