Quartzite
Quartzite is a hard metamorphic rock formed from quartz-rich sandstone, in which the sand grains have recrystallized into an interlocking mosaic of quartz. It is white, pink, grey or purple, and it breaks through the grains rather than around them.
Quartzite is a hard metamorphic rock formed from quartz-rich sandstone, in which the sand grains have recrystallized into an interlocking mosaic of quartz. It is white, pink, grey or purple, and it breaks through the grains rather than around them.
🪨 Geology Guide Specimen: Open Metaquartzite (Quartzite) in the CRV Science Rock & Mineral ID Guide to log the specimen, compare it with the other 6 subgroups of Metamorphic, and test your eye in LithoClade.
Recrystallization: How Does Sandstone Become Quartzite?
Heat and pressure make the quartz grains of a sandstone grow into one another and fuse, destroying the original pores. Geologists also use "orthoquartzite" for a quartz sandstone cemented by silica that was never metamorphosed, so the key test is fracture: true quartzite breaks across the grains, in smooth surfaces, while sandstone breaks around them.
Colors: Why Is Quartzite Pink or Green?
Pure quartzite is white. Traces of hematite make it pink or red, and a chromium-rich mica called fuchsite gives green quartzite. Iron and manganese give other shades.
Ridges and Resources: Why Does Quartzite Stand Out?
Quartzite is very resistant to weathering, so it forms the crests of many mountain ridges, such as those in the Appalachians. It is quarried for crushed stone, railway ballast and as a source of pure silica. See quartz arenite, the sandstone it forms from, and quartz.
Quartzite at a Glance
| Property | Value |
|---|---|
| Type / variety | Granoblastic Recrystallized Silica Quartzite |
| Composition | >95% Interlocking Recrystallized Quartz (SiO₂) ± Trace Hematite/Fuchsite |
| Geology Guide group | Metamorphic Rocks (Foliated, Granoblastic & High-P) |
| Rock Classification | Non-Foliated (Granoblastic & Contact) |
| Mohs hardness | Mohs 7 (scratches steel easily; does not fizz in acid) |
| Texture / habit | Equigranular interlocking sutured crystal mosaic lacking foliation |
| Density | 2.65–2.70 g/cm³ |
| Lustre and cleavage | Sugary-to-vitreous white, pink, or purple; fractures straight THROUGH grains |
| Geological setting | Contact or regional recrystallization of quartz sandstone protoliths |
| Diagnostic feature (Geology Guide) | Extremely hard (Mohs 7), sugary-lustred white, pink, or purple rock lacking any cleavage planes; when broken with a hammer, the fracture slices straight through the fused silica grains rather than around them. |
| Protolith | Quartz arenite |
| Fracture | Through the grains |
See Also
- Quartz Arenite — the sandstone parent
- Quartz — the mineral it is made of
- Marble — the carbonate counterpart