01 / Geological family
Origin and composition
- Geological family
- Igneous
- Origin and composition
- Ignimbrite, rhyolitic tuff with hematite and lapilli
- Origin
- Rochlitz Mountain, Saxony, Germany
- Appearance and identification
- Red-pink with purple lapilli and pale veins
Igneous rocks form when molten material solidifies. Cooling underground can produce visible crystals, as in granite; cooling at the surface can produce fine grains, cavities or porphyritic textures. Basalt, granite and many porphyries illustrate different compositions and structures. The commercial term granite can also include other geological rock types: a specification benefits from both the trade name and petrographic description.
02 / History and curiosities
History and curiosities
Romanesque portals and Saxon monuments document centuries of use in construction and sculpture.
03 / Applications and design
Applications and design
Documented uses include building blocks, columns, tracery, sculpture and restoration.
Finishes and processes ↗04 / Technical interpretation
What to ask your supplier
The name porphyry does not make it equivalent to compact paving porphyry; it is a pyroclastic rock.
05 / Care and maintenance
Care and maintenance
Remove dust and grit with soft tools, wash with a compatible neutral cleaner, then rinse and dry. Identify composition before using stain or scale removers: carbonate stones are acid-sensitive. Test every treatment in an inconspicuous area. An impregnator can reduce absorption but does not make a material waterproof or stain-proof.
Thoughtful cleaning, protection and maintenance ↗07 / Sources and further reading
