pitchstone

• Rocha vulcânica vítrea de composição granítica, geralmente escura, cujo aspecto lembra resina ou pez.

A dark, glassy volcanic rock of granitic composition, resembling pitch in appearance.

1. Dark acid granitic glassC2formalscientific

   A natural volcanic glass with a dark, resinous or pitch-like luster, typically composed of acidic magma.

   Vidro granítico ácido escuro

   • The geologist identified the sample as pitchstone due to its characteristic dark, glossy surface.
   • Pitchstone is often found in volcanic regions where acidic lava cooled rapidly.
   • Unlike obsidian, pitchstone has a higher water content and a duller, more resinous appearance.