From lava flow to hand specimen
Relating desk-scale fragments to obsidian domes, talus, pumice, and cooling lava.
Complete archive
Field notes
Six concise entries on the visible properties of volcanic glass, written for careful looking rather than collecting advice or specimen appraisal.
Photographing a nearly black surface
A simple reflected-light method for showing luster without flattening texture.
Obsidian and basalt are both dark—then the similarities end
Comparing grain, luster, fracture, composition, and common formation settings.
What makes the “snowflakes”?
Pale spherulites and the slow process by which volcanic glass devitrifies.
Reading a conchoidal fracture
Curved surfaces, ripple marks, bulbs, and the absence of crystal cleavage.
On edge reflections in black volcanic glass
A first observation about thin highlights and hidden fracture curves.