Obsidian igneous rock, teaching, school education, uk seller

All of our Rocks are 100% Genuine Specimens & come with a Certificate of Authenticity
Specimen: Obsidian
Type: Igneous Rock
Location: Norway
Size:  24 x 26 x 64mm (0.94 x 1.02 x 2.52 inches)

Obsidian is a naturally occurring volcanic glass formed as an extrusive igneous rock.
It is produced when felsic lava extruded from a volcano cools rapidly with minimal crystal growth. Obsidian is commonly found within the margins of rhyolitic lava flows known as obsidian flows, where the chemical composition (high silica content) induces a high viscosity and polymerization degree of the lava. The inhibition of atomic diffusion through this highly viscous and polymerized lava explains the lack of crystal growth. Obsidian is hard and brittle; it therefore fractures with very sharp edges, which were used in the past in cutting and piercing tools, and it has been used experimentally as surgical scalpel blades.
Igneous rocks are formed either deep underground within the earth, when magma becomes trapped in small pockets and slowly cools down to a solid form, Or above ground after volcano eruptions when lava cools down and becomes a solid form. Common types include Granite, Basalt, Gabbro, Pumice and Rhyolite.

ACTUAL AS SEEN: The image shows the EXACT specimen you will receive. The specimen has been carefully hand selected and photographed. Measurements are as accurate as possible, though be aware measuring precise dimensions can be difficult from irregular shaped items. Whilst we portray colours as close to life-like as we can, colours will vary if taken in sunlight, indoors, from monitor to monitor and device to device. Once this specimen is sold, we will update this listing with new similar selected item, with a new photo and dimensions.