Everything about Pumice totally explained
Pumice is a textural term for a volcanic rock that's a solidified frothy lava composed of highly
microvesicular glass
pyroclastic with very thin, translucent bubble walls of
extrusive igneous rock. It is commonly, but not exclusively of silicic or felsic to intermediate in composition (for example rhyolitic, dacitic, andesite, pantellerite, phonolite, trachyte), but occurrences of basaltic and other compositions are known. Pumice is commonly pale in color, ranging from white, cream, blue or grey, but can be green brown or black. It forms when gases exsolving from viscous magma nucleate bubbles which can't readily decouple from the viscous magma prior to chilling to glass. Pumice is a common product of explosive eruptions (plinian and ignimbrite-forming) and commonly forms zones in upper parts of silicic lavas. Pumice has an average
porosity of 90%, and initially floats on water.
Scoria differs from pumice in being denser, with larger vesicles and thicker vesicle walls; it sinks rapidly. The difference is the result of the lower viscosity of the magma that formed scoria. When larger amounts of gas are present, the result is a finer-grained variety of pumice known as
pumicite. Pumice is considered a
glass because it has no
crystal structure. Pumice varies in density according to the thickness of the solid material between the bubbles; many samples float in
water. After the explosion of
Krakatoa, rafts of pumice drifted through the
Pacific Ocean for up to 20 years, with tree trunks floating among them. In fact, pumice rafts disperse and support several marine species. In 1979, 1984 and
2006, underwater volcanic eruptions near
Tonga created large
pumice rafts, some as large as 30
km that floated hundreds of miles to
Fiji.
There are two main forms of vesicles. Most pumice contains tubular microvesicles that can impart a silky or fibrous fabric. The elongation of the microvesicles occurs due to ductile elongation in the volcanic conduit or, in the case of pumiceous lavas, during flow. The other form of vesicles are subspherical to spherical and result from high
vapour pressure during eruption.
Uses
Pumice is widely used to make lightweight
concrete or insulative low-density 'breeze-block' type bricks. When used as an additive for
cement, a fine-grained version of pumice called
pozzolan is mixed with
lime to form a light-weight, smooth, plaster-like
concrete. This form of concrete was used as far back as
Roman times.
It is also used as an
abrasive, especially in polishes, pencil
erasers,
cosmetic exfoliants, and to produce
stone-washed jeans. "Pumice stones" are often used in
salons during the
pedicure process to remove dry and excess skin from the bottom of the foot as well as calluses. Finely ground pumice is added to some toothpastes and heavy-duty hand cleaners as a mild abrasive. Perhaps the most famous product advertised to contain pumice is
Lava soap. It is a heavy-duty hand soap, sold in both bar and liquid form, for cleaning deep into the finger prints.
Further Information
Get more info on 'Pumice'.
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