Hierarchy classification:

1. top of the aat hierarchies
2. Materials Facet
3. Materials (hierarchy name)
4. materials (substances)
5. [materials by composition]
6. inorganic material
7. rock (inorganic material)
8. igneous rock
9. [igneous rock by composition]
10. [igneous rock by composition: physical]

Narrower term/s

• quartz porphyry [NP][+]
  • elvan
• red antique porphyry

Anotations

Scope note:

A dark purplish-red rock, first quarried in ancient Egypt, containing relatively large crystals in a fine-grained igneous matrix. One of the hardest rocks, it takes a high polish and is valued as a durable sculptor's material and as a decorative architectural material. It is considered the best material for the muller and slab used for grinding artists' colors.