Having a low water content when newly formed, typically less than 1% water by weight, obsidian becomes progressively hydrated when exposed to groundwater, forming perlite.
Pure obsidian is usually dark in appearance, though the color varies depending on the presence of impurities.
Obsidian is produced when felsic lava extruded from a volcano cools rapidly with minimal crystal growth.
It is commonly found within the margins of rhyolitic lava flows known as obsidian flows, where the chemical composition (high silica content) induces a high degree of viscosity and polymerization of the lava.
These bubbles can produce interesting effects such as a golden sheen (sheen obsidian).
An iridescent, rainbow-like sheen (rainbow obsidian) is caused by inclusions of magnetite nanoparticles.
I’ve just been too busy building flat cars for the slate quarry. The kit was for SR&RL boxcars 67-76, which were 28-foot cars.
The inhibition of atomic diffusion through this highly viscous and polymerized lava explains the lack of crystal growth.
Obsidian is hard and brittle and therefore fractures with very sharp edges.
However, I decided to do something different – one can only build so many flat cars in a row, after all – so a while ago I started work on an NJ International wooden kit (acquired from another friend who was selling off his On2 equipment… I modeled it as Somerset & Piscataquis Counties #68. The kit included all the basics, but was missing information like how to route brake rods and pipes, and many details like the dozens of NBWs used on grab irons, etc.
Plus, of course, a tin roof made of individual panels of thick embossing tin. It’s “finished”, although I’m waiting for some air hoses to add to the ends.
Canada, Chile, Georgia, Greece, El Salvador, Guatemala, Iceland, Italy, Japan, Kenya, Mexico, New Zealand, Papua New Guinea, Peru, Scotland, Turkey and the United States.