igneous
Porphyritic Basalt with K-Feldspar Phenocryst
Porphyritic Basic Igneous Rock (with Potassium Feldspar)
Hardness: 6-6.5; Color: Dark grey to charcoal matrix with a distinct pink/reddish heart-shaped phenocryst; Luster: Dull/earthy (matrix) to vitreous (crystal); Structure: Porphyritic (large crystals in fine-grained matrix).
- Hardness
- 6-6
- Luster
- Dull/earthy (matrix) to vitreous (crystal)
Identified More igneous →
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Physical properties
Hardness: 6-6.5; Color: Dark grey to charcoal matrix with a distinct pink/reddish heart-shaped phenocryst; Luster: Dull/earthy (matrix) to vitreous (crystal); Structure: Porphyritic (large crystals in fine-grained matrix).
Formation & geological history
Formed through a two-stage cooling process of magma: initial slow cooling deep underground allowing the pink feldspar crystal to grow, followed by a rapid eruption or movement to a cooler environment where the fine-grained dark matrix solidified.
Uses & applications
Primarily of interest to mineral collectors and geologists as a textbook example of porphyritic texture. Basalt is used in construction as aggregate.
Geological facts
The heart-shaped appearance of the pink mineral is a coincidence of how the rock was naturally weathered and eroded into a river pebble. These are common in glacial till and river beds in volcanic regions.
Field identification & locations
Identify in the field by looking for a fine-grained, dark volcanic matrix containing large, distinct, angular or shaped mineral crystals of a different color. Found commonly in Lake Superior basalt deposits or volcanic river beds.
