Pumice rock is volcanic glass that can be thought of as spongy lava.
Pumice, although textually classified as a rock, is a volcanic glass that is formed when molten lava cools, depressurizes and solidifies rapidly into a froth-like mass. It can be thought of as spongy lava. Pumice has an average porosity of approximately 90 percent and can easily float on water.
Pumice Rock Deposits
Pumice is mined from deposits in Hungary, Canada, British Isles, Greenland, New Zealand, Iceland and the Lipari Islands. According to Keith Branigan and Patrick Foster in the book "Barra: Archaeological Research on Ben Tangaval," the largest deposits of pumice are mined from archaeological sites of Scotland and Norway.
According to the Society for Mining, Metallurgy, and Exploration (U.S.) in the report titled "Industrial Minerals & Rocks: Commodities, Markets, and Uses," pumice rock deposits are broadly classified into four types: reworked (epielastic), pyroelastic flows, air-fall deposits and flows and domes. There are various gradations between each of the four types.
Pumice Physical and Chemical Properties
Pumice is an inert material composed primarily of aluminum oxide and silica, but may contain trace amounts of calcite, metal oxides and salts.
Pumice is considered a glass due to its lack of crystal structure. It is lightweight, and has a bulk density that ranges between 0.4 to 0.8 grams per cubic centimeter. According to Michael Raviv and Johann Heinrich Lieth in the book "Soilless Culture: Theory and Practice," pumice rock has a total porosity that ranges between 70 and 85 percent of the weight of the stone.
Pumice provides good heat, cold and sound insulation. It has excellent fire resistance and does not change its form or volume even at temperatures exceeding 1382 degrees Fahrenheit.
The specific gravity of pumice is 0.64 (its mass compared with the mass of water), making it lighter than water. It has a refractive index of 1.5 and is rated 6.0 on the Mohs hardness scale.
Pure pumice can be grey, blue, cream, white or black.
Types
Commercially used pumice rock is commonly classified as pumice powder (ranging in size from 0 to 160 microns), pumicite (ranging in size from 3 millimeters to 20 millimeters) and textile graded pumice (ranging in size from 1 to 7 centimeters).
Uses
Pumice rock is typically employed in construction for the manufacture of lightweight structural materials, such as concrete and concrete blocks. It is also used in horticulture, abrasives and landscaping. Pozzolan, a type of pumice, is used to make lightweight, fine-grained cement that is applied on building interiors and to make floors.
Pumice is used as a filler in paints, rubber, hot asphalt mixes, mold release compounds and plastics. It is also used as an absorbent in acid washing, potting soils and floor sweep.
Advantages
Pumice is inert and temperature variations, excessive heat, microorganisms or acids do not affect its stability. It is environmentally friendly and its recycling possess no major problems.
Tags: pumice rock, ranging size, ranging size from, size from, also used, four types, glass that