Obsidian is a naturally occurring volcanic glass that develops when the lava that has been ejected from a volcano rapidly cools down with little crystal formation. It’s made of igneous rock.
The lighter elements silicon, oxygen, aluminium, sodium, and potassium are abundant in felsic lava, which is used to make obsidian. Obsidian flows, which are rhyolitic lava flows, frequently contain them along their borders.
These flows are highly viscous due to their high silica concentration. The high viscosity of the lava prevents atoms from diffusing through it, which prevents the nucleation process that leads to the production of mineral crystals. This causes the lava to naturally cool quickly and condense into the glass.
How hard is Obsidian?
Obsidian has a usual hardness of 5 to 5.5 on the mineral hardness scale, making it moderately soft. In contrast, the hardness of quartz (crystallized silicon dioxide) is 7.0.
Obsidian only appears where the volcanic activity takes place and where a silica-rich magma has a high chemical composition.