On edge reflections in black volcanic glass
Why a nearly black specimen can suddenly reveal curved fracture lines when the light moves a few degrees.
Read note →Independent mineral notebook
Glass made by a volcano.
Short, source-linked observations on obsidian: how it breaks, how it reflects light, and what its textures record about cooling lava.
Recent entries
Notes from the work table
Each entry starts with one visible detail and follows it into the geology, handling, or photographic method behind the specimen.
Reading a conchoidal fracture
Curved scars, ripple marks, and sharp edges are consequences of glass lacking an orderly crystal lattice.
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What makes the “snowflakes”?
The pale patches in snowflake obsidian record devitrification: glass slowly reorganizing into crystals.
Read note →Working method
Look slowly.
Label clearly.
- Light
- One soft source, moved deliberately
- Scale
- Hand specimen before magnification
- Language
- Observation separated from inference
- Sources
- USGS, NPS, and museum records
More from the archive
Objects and landscapes
Obsidian makes more sense when the polished piece, the fractured edge, and the lava dome are considered together.
Obsidian and basalt are both dark—then the similarities end
A practical comparison of luster, grain, fracture, and the very different magmas that commonly produce them.
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Photographing a nearly black surface
Use reflected shape rather than raw brightness to reveal a glassy surface without turning it grey.
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From lava flow to hand specimen
The tidy object on a desk begins in a rough landscape of viscous lava, rubble, pumice, and weathering.
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