igneous
Porphyritic Andesite
Andesite with Hornblende phenocrysts
Hardness: 6-7 (Mohs). Color: Gray to tan fine-grained groundmass with dark needle-like crystals (phenocrysts). Luster: Dull (matrix) to vitreous (crystals). Structure: Porphyritic. Specific Gravity: 2.4-2.8.
- Hardness
- 6-7 (Mohs)
- Luster
- Dull (matrix) to vitreous (crystals)
Identified More igneous →
Explore Porphyritic Andesite in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 6-7 (Mohs). Color: Gray to tan fine-grained groundmass with dark needle-like crystals (phenocrysts). Luster: Dull (matrix) to vitreous (crystals). Structure: Porphyritic. Specific Gravity: 2.4-2.8.
Formation & geological history
Formed through the rapid cooling of intermediate lava at the Earth's surface, allowing smaller crystals to form a matrix around larger, pre-formed hornblende or pyroxene crystals.
Uses & applications
Used primarily in construction for crushed stone, road base, and occasionally as decorative stone or landscaping rock.
Geological facts
The name 'Andesite' is derived from the Andes Mountains where this type of volcanic rock is extremely common at the edges of continental plates.
Field identification & locations
Identify in the field by the 'porphyritic' texture where large dark crystals are suspended in a much finer-grained, lighter-colored uniform matrix. Common in volcanic arc regions.
