igneous

Porphyritic Basalt (Chinese Writing Stone)

Porphyritic Basalt or Porphyritic Andesite

Hardness: 6-7 (Mohs scale), Color: Dark grey to black matrix with white or lighter grey lath-like phenocrysts, Luster: Dull to sub-vitreous, Crystal structure: Aphanitic (fine-grained) matrix with visible elongated crystals, Specific gravity: ~2.8-3.0

Identified April 7, 2026More igneous →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Formation & geological history

Formed when basaltic magma cools in two stages: first, large crystals (phenocrysts), often feldspar, grow slowly underground; then, the remaining magma erupts and cools rapidly on the surface, trapping the large crystals in a fine-grained matrix.

Uses & applications

Used primarily as decorative stone, lapidary material for jewelry (cabs, beads), and garden ornaments. In larger quantities, basalt is used for crushed stone in construction.

Geological facts

This specific texture is often called 'Chinese Writing Stone' or 'Letter Stone' because the randomly oriented, elongated feldspar crystals resemble calligraphy characters.

Field identification & locations

Identify in the field by looking for distinct, pale, needle-like or rectangular crystals embedded in a much darker, fine-grained volcanic rock. Often found in areas of past volcanic activity, notably in California, USA and parts of China.

Other igneous specimens

See all

Blue Apatite

Fluorapatite (Ca5(PO4)3F)

mineral

Dark Igneous Rock (Likely Basalt or Diabase)

Basalt (extrusive igneous rock) or Diabase (intrusive igneous rock - also known as Dolerite), largely composed of plagioclase feldspar, pyroxene (augite), and sometimes olivine and amphibole. Exact mineralogy would require thin section analysis.

Igneous

Magnetite

Iron(II,III) oxide (Fe3O4)

mineral

Blue Apatite

Apatite (Group), Ca5(PO4)3(F,Cl,OH)

mineral

Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

mineral

Magnetite

Magnetite (Fe3O4)

mineral