Pumice

Pumice or pumice (via OHG pumi ȥ / bume ȥ from the Latin Pumex ) is a porous glassy volcanic rock whose density is due to the numerous pores, which constitute a substantial part of the volume is less than that of water. Its color can vary greatly: pumice from basaltic lava with large bubbles is almost black and is called rock foam, with increasing air content and decreasing bubble size, the color is lighter, so that almost white pumice is possible ( as in the north of Lipari or Stromboli ), as well as all intermediate tones ( as yellow - gray). Eventually, the pore boundaries penetrating can (also colored ) occur retention such as volcanic glass and crystals.

Formation

Pumice is produced by gas-rich volcanic eruptions in which viscous lava is foamed by the water vapor and carbon dioxide. Chemically pumice is no different from other lava ( the chemistry can just as strong as in lava vary), however, he is significantly lighter ( has about a third of the density) and has due to the caused by volcanic gases pores often a much lighter color than lava with the same composition.

Rock foam is formed from basaltic lava and is almost black. It is glassy and takes on the appearance of large pore sponges to. By enclosing the gas bubbles rock foam is lighter than water and it is very fragile. This rock is not to be confused with pumice; even with obsidian, although it has the same chemical composition. Rock foam has a completely different look than pumice and the edges are sharp. It is relatively rare and occurs only partially in small quantities. It is adjacent to pumice a rock that floats on water.

Occurrence and degradation

Pumice is mined in Germany in the area of the Laacher lake and near Neuwied. In the Neuwied Basin, between the Eifel and the Rhine at Koblenz, he stores under thick layers of loess. To reduce the loess is set aside on the most arable crops, encouraged the pumice in the open pit and then again reclaimed the area with the loess soil. Therefore, the degradation of pumice, other than be destroyed by lava, for the valuable biotopes, little harmful to the environment.

Pumice, by rather constant land - erosion discharge into the sea but also by acute volcanic eruption. The particularly large eruption of Tambora in Indonesia in 1815 threw so much pumice into the sea, that even years later ships collided on floating pumice islands. In August 2012, 50 km driving light pumice was sighted between New Zealand and Tonga on a sea area of ​​more than 400 x, which is attributed to the underwater volcano Monowai.

Use

• Pumice is used for the production of lightweight concrete blocks and Rhenish Calc, because he has a good thermal insulation capacity.
• Pumice is a basic or aggregate for horticultural substrates and is suitable for the improvement of soils. It improves the pore structure and thus the aeration, water holding capacity and root penetration. Pumice is the easiest course pored raw material in horticulture. Due to its high water storage capacity makes it suitable for use in green roofs.
• He was crushed fine formerly used as abrasives for wood and pore-filling additive in the shellac polish.
• In dental technology, is pumice, different grain sizes, for pre-polishing of plastic work (about full and partial dentures ) are used, and in addition to sodium fluoride as part of Fluoridierungslackes Duraphat.
• Pumice is used in the manufacture of jeans, to produce the " stone-washed " effect.
• Handy pumice stones are offered for foot care and for grinding excess cornea.
• With larger pumice plaster can be ground.
• With pumice, about from the pharmacy, silver rings can again matted or wood and paintwork to be ground.
• Pumice is used in different grain sizes, eg 0.6 to 1.6 mm as a filter material in water treatment.
• In pumice corals are bred artificially. To this end, we hung Bimssteinblöcke for 8 months on a reef near the village Tagaqe in Fiji, so that seaweed and invertebrates on the reef could build colonies.

History

Pronounced was the use of pumice from the earliest times in Crete, where the sea constantly BC especially anschwemmt pumice from the volcanic neighboring islands, since the second half of the 16th century, Santorini ago. Paul Faure reported that 15 types of use existed. The coastal people gathered among others, the alluvial pumice stones as building material, cleaning agents, degreasing agents in the pottery to stop as a remedy for ulcers and drunkenness and the fermentation. In small bowl, he was also sacrificed to the gods, as the gods of the port Nirou Chani, where. Arkalochori in the area of the great sacred cave of the place and the gods of the city and harbor Cydonia The gray pumice considered the Cretans as male, white as a female.

In ancient times, the pumice stone to body care, for the treatment of the sick, for sharpening the pen and smoothing of parchment leather was used for books. In Spain and Asia bricks were made ​​for the construction of bimssteinhaltiger clay.

In the Preface to the Critique of Practical Reason, Kant used the Latin term " ex pumice aquam " which means something like: " press from pumice water ", which he accuses those people who want to squeeze out experience sets necessity judgments.

Different color pumice

In the close-up of the sponge-like pore structure of the pumice is easy to see