other names: Pumice, Schaumstein, Pumex, Pumice
mineral class: ?
chemical formula: approximately SiO2 + Fe + Al + C + Na + Mg + Ca
Chemical elements: Silicon, oxygen, iron, aluminum, carbon, sodium, magnesium, calcium
Similar minerals: Obsidian
colour: white, yellow, gray, black, brown
crystal structure: /
mass density: ?
Mohs hardness: approx. 4.5
stroke color: ?
use: Building material
General to the pumice:
pumice or pumice describes a porous volcanic rock, which has an extremely low weight. The density of pumice is significantly smaller compared to water, which is due to the many different sized pores and means that rock parts of different sizes can easily swim. Pumice can form from all types of magma and thus develops from basalt, as well as from dacite, ryolite or andesite, with acidic rocks favoring the formation of the characteristic porous structure with many voids. Depending on the composition, pumice may appear both white and pale yellow, as well as gray, brown or almost black. However, most types of pumice are of significantly lighter color due to the porous structure compared to lava of the same chemical composition.
Occurrence and localities:
The characteristic, pervious structure of the pumice is caused by explosive volcanic eruptions, in the course of which in the air thrown magma by a high gas content, a distinct blistering. These gas bubbles cause the viscous rock slurry to literally foam up and become a kind of hard and sponge-like foam when it solidifies quickly.
The most important place in the world where pumice is mined is on Lipari, a Sicilian island, where a huge eruption of Mount Pelato brought large amounts of magma to the earth surface 1400 years ago. Today, almost a fifth of the entire island is covered by pumice, which is mined in huge quarries and transported from there to the entire world. In addition to the Mediterranean, the versatile volcanic rock is also promoted in Central Europe, in Asia and on all other continents.
History and usage:
The intensive use of pumice is already known from the 16th century BC, when the people of the Greek islands used the large quantities of alluvial boulders both as building material for houses, cleaning agents and for sharpening writing implements, as well as in personal hygiene and as a general purpose remedies. Even today pumice is used in foot care for the removal of calluses, in construction as a material for thermal insulation and for the production of lightweight building blocks and cement as well as abrasives and polishes use. Milled is pumice available as a powder, which is suitable for cleaning dentures as well as for polishing tarnished silver, plaster, wood and shellac. In the textile industry, it is especially worth mentioning its use for the treatment of jeans, which is responsible for the popular wash effect in denim. Due to its porous structure, the rock is ideal as a water-storing substrate for plants that can easily root in it and find good support. In Fiji, an attempt was made to breed corals on giant pumice blocks so that animals and underwater plants can form a new ecosystem there.