The 3D model represents an igneous rock with a glassy texture, there are no crystals inside.
The rock has smooth and shiny lustre, with some tiny and clear bands, the borders are sharp and cutting, the shape is similar to an arrowhead.
Apparently, the rock is an obsidian.
This type of texture is generally obtained through a magmatic process, it is formed through the solidification of the magma. This event may occur with different speed, so there are two classes of magmatic rock: extrusive and intrusive. The extrusive igneous rocks are formed with a fast or very fast cooling, as happened to our rock: instead, intrusive rocks are formed with a long cooling process, which may last thousand years. The division between intrusive and extrusive rocks is not only due to the cooling rate but it also depends on the properties of the magma: acidity, viscosity and temperature. Probably our rock is the result of the cooling of an acidic magma witch has low viscosity.
Our rock is an obsidian, so it may have been produced after a volcanic eruption, and the fast cooling may be due to the contact with water. When the lava reaches a large quantity of water, the water absorb its heat and then the lava solidifies quickly producing obsidian.
| Obsidian physical property | |
| Density | 2-3 g/cm3 |
| Hardness | 5-6 |
| Cleavage | Absent |
| Fracture | Conchoidal |
| Color | Deep black |
| Luster | Vitreous |
| Optical properties | Translucent |
| Occurence | Quite common |
Obsidian is currently used to produce mineral wool, a sort of glass made of thin fibres, created by melting obsidian at 1300°C. It is also used for ornamental purpose. During the past, the Aztec used obsidian to obtain arrowheads, knives and razors. Even today obsidian blades are produced for surgical uses, in fact some surgeons prefer obsidian to steel because of its clean cut and the lack of metallic particulate, that can cause allergy.
Plinio named it “lapis obsidianus” in honor of Obsidius, who first mentioned the rock in some areas of Etiopia. Some discoveries suggest the knowledge of the rock in ancient times: in the nuragic, in the ancient Egyptian and in pre-Colombian civilizations.
Carmine Piras, contemporary sardinian sculptor, famous all over Europe, is the father of obsidian sculpture and founder of obsidian museum in Pau. Established master in every field of sculpture, he has drawn inspiration for his works by nuragic art, born and developed in Sardina, since the bronze age up to the II century A.D. Among others materials the nuragic folk used obsidian, as there was a big vein close to Oristano. We can admire some statues, masks and weapons of his, crafted with obsidian, in the following pictures.
Nicoló Malvestiti 2021