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Rock and Mineral Dictionary
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

Click on an underlined word for more information on that subject.
If the rock or mineral term you are looking for is not in the dictionary, please e-mail us and we'll add it.

P



Pacific cat's-eye

Pacific cat's-eye is the operculum of a sea snail called the Turban Shell (Turbo petholatus, found in the South Seas north of Australia). The operculum is part of many shelled animals - it is the calcified, disc-shaped "trap door" that opens and closes to protect the animal inside its shell. The Turban Shell's operculum is an eye-like disc with a natural cabochon shape - it is used in jewelry. This jewelry was popular in Victorian Era Britain.


padparadscha sapphire

Padparadscha sapphires (also spelled padparadschah) are a rare pink-orange variety of corundum or the synthetic equivalent. These gems are mined in Sri Lanka and are usually heat treated to improve and intensify the color. The name padparadscha comes from the Sinhalese word for lotus flower. Hardness = 9, Specific Gravity = 4.

pahoehoe

Pahoehoe (pronounced "pah-hoy-hoy") is a Hawaiian term for lava that, when solid, has a smooth or rope-like surface.


paleontology

Paleontology is the branch of biology that studies the forms of life that existed in former geologic periods, chiefly by studying fossils.


paleontologist

A paleontologist is a scientist who studies paleontology, the forms of life that existed in former geologic periods, chiefly by studying fossils.
Paleozoic era
The Paleozoic era (540 to 245 million years ago) saw an explosion of new life forms. It ended with the largest mass extinction in history and was followed by the Mesozoic Era.


palladium

Palladium is a valuable, durable, and malleable light-gray metal used in some jewelry; it is related to platinum, but is less dense and has a lower melting point. Unlike platinum, palladium reacts when exposed to aqua regia, sulfuric, nitric, and hydrochloric acids. It also develops a tarnish when it is heated. Pallasium is not a shiny as platinum. Palladium was only isolated as an element in 1802 by William Hyde Wollaston and Smithson Tennant. It was first used in jewelry in 1939 (during World War 2, platinum was used for war purposes, and was not available for jewelry making - palladium was temporarily used as a substitute for platinum). White gold is sometimes alloyed with palladium (instead of nickel), resulting in a gray-white gold. After World War 2, palladium was rarely used in jewelry making beacuse of some difficulties in working with it. Palladium was recently discovered to be useful in engine catalytic converters, and its price skyrocketed to over $700 per ounce (it had previously been much less expensive than platinum or gold) and is no longer practical to use as jewelry.

Pangaea

Pangaea was a supercontinent consisting of all of Earth's land masses. It existed during the Permian and Jurassic period. It began breaking up during the Jurassic period, forming continents Gondwanaland and Laurasia, separated by the Tethys Sea.

patina

Patina is the change of an object's surface layer that result from aging. Exposure to the air for an extended period of time oxidizes many metals, turning copper and bronze green, and gold reddish. Artificial patinas can be applied to newer objects by using acids or electrolytes.

pearl opal

Pearl opal (also called Tabasheer or tabashir opal) is an organic stone that forms in damaged joints (nodes) of bamboo plants. This hydrated form of silica appears as a rounded mass of opal, and looks like seed pearls.


Peking jade

Peking jade is the same as jade, but often refers to nephrite.

Pele's hair

Pele's hair is a Hawaiian term for natural spun glass that can be as much as 2 m long. It is formed from the fountaining of fluid basaltic lava, cascading lava falls, or from turbulent lava flows.

period

The period is the basic unit of geological time in which a single type of rock system is formed, lasting tens of millions of years.


peridot

Peridot (also known as the "evening emerald" and chrysolite) is a yellow-green semi-precious stone with an oily luster; peridot is a transparent, green form of olivine. Peridot exhibits double refraction; when you look through the stone, things appear double. For example, when looking into a faceted peridot gemstone, the number of bottom facets appears to be double the actual number of facets. Most peridots are from a volcanic island in the Red Sea, Zebergit/St. John, the "Serpent Isle." Peridots have been found in meteorites. Peridot has a hardness of 6.5. Peridot cat's eye also exists.

Permian period

Also known as "The Age of Amphibians" (280 to 245 million years ago), this is the time when Pangaea formed and Earth's atmosphere was oxygenated to modern levels. It ended with the largest mass extinction and was followed by the Mesozoic Era. Ancient sharks swam the seas during the Permian period.


petrified wood

Petrified wood (also called xyloid jasper or jasperized wood) is wood that has fossilized - all the original chemicals in the wood have ben replaced with minerals, making a stone-like replica of the original wood.


phases of matter

Matter can exist in four phases (solid, liquid, gas, and plasma) and a few other extreme phases, like critical fluids and degenerate gases. The phase diagram of water (above) shows its phase at various temperatures and pressures.


physical map

A physical map is a map that shows an areas natural physical features, like mountains, lakes, and rivers.

pillow lava

Pillow lava is lava that cools under the sea, with an interconnected, sack-like form.

pink topaz

Pink topaz (Aluminum silicate fluoride hydroxide) is a very hard pink gemstone. Pink topaz is usually created by irradiating common yellow topaz. Topaz has a hardness of 8 and a specific gravity of 3.5-3.6.

plane of symmetry

A plane of symmetry is a plane that divides a solid into two mirror-image pieces of the solid.


plateau

A plateau is a large, flat area of land that is higher than the surrounding land.


plates

The crust of the Earth is broken into plates. The plates are enormous chunks of rock that float atop the soft mantle. The plates are moving at a speed that has been estimated at 1 to 10 cm per year. Oceanic plates (those that are under the ocean) are thinner and denser than continental plates.
Continental Drift
Forward Backward

plate tectonics

Plate tectonics is the now-established theory that chunks of the Earth's crust (plates) float on the surface and change both position and size over time.


plutonic formation

A plutonic formation (also called a laccolith or an igneous intrusion) is a formation in which magma (molten rock) is trapped beneath the surface of the Earth and pushes the rock located above it into a dome shape. It has a flat base and a convex upper surface. The magma cools and solidifies, and eventually, it is exposed (as the fractured sedimentary rock above it erodes away).


platinum

Platinum is a very strong, dense precious metal with a white color. Platinum jewelry is usually 90%-95% pure, is very sturdy, and holds stones well. Platinum is related to iridium. Platinum is 60% heavier than gold. Iridium and platinum are frequently alloyed together, since the Irridium increases the workability of the platinum. Platinum was only discovered in the 1700's in Russia. Platinum is abbreviated Pt. and Plat.


pleochroism

Pleochroism is the property of having more than two colors, especially when viewed from different angles. In pleochroic minerals, a single stone will show many colors (in the case of Iolite, violet-blue, light blue, and yellow-gray will be visible).

plug

A plug (also called a volcanic neck) is solidified lava that fills the conduit of a volcano.

point

A point is a hundredth of a carat or 0.002 gram.

porous

Porous stones have tiny holes in them. These holes allow water, oils, and other substances to penetratethe stone, frequently changing their appearance over time. Many stones are porous, including turquoise.

prase opal

Prase opal is a green, translucent opal that looks quite similar to chrysoprase (hence the name "prase") or jade. This type of opal is found in Tanzania, Africa. This gem does not display the iridescence found in some opals.

precious stone

A precious stone (also called a gemstone) is one that is valuable and rare.

Precambrian

The Precambrian is the time 540 before the Cambrian period (before million years ago). It is the time from when the Earth formed until simple life-forms evolved.

precipitation

Precipitation is rain, sleet, hail, snow, or other condensation products falling from the atmosphere. Precipitation on Earth is is key in the water cycle.

prehistoric

Prehistoric refers to the time before people began recording history in writing. This time varies from culture to culture.
pumice
Pumice is a light-weight, spongy rock that is formed in explosive volcanic eruptions. This igneous rock is light and porous, containing a network of gas bubbles in volcanic glass and minerals. Pumice can form from any types of magma, including basalt, andesite, dacite, and rhyolite.


purple diamond

Purple diamonds are rare, fancy diamonds and are quite valuable. Diamonds are precious, lustrous gemstones made of highly-compressed carbon; they are one of the hardest materials known. Diamonds have a hardness of 10, a specific gravity of 3.5, and a refractive index of 2.417 - 2.419.


pyrite

Pyrite (also known as fool's gold) is a shiny, metallic mineral that is a form of iron. Marcasite stones come from pyrite.
pyroclastic
Pyroclastic (meaning "fire fragmented") refers to broken-up rocks, pumice, ash, and other bits of material that are formed in a volcanic eruption.
pyroclastic flow
A pyroclastic flow is an avalanche of pyroclastic materials (broken rocks, pumice, and ash) and hot gases that erupts from within a volcano. A pyroclastic flow travels at up to 100 miles per hour. Within the flow, temperatures can reach 500 degrees C.


pyrope garnet

Pyrope garnet is the familiar deep red garnet. Red garnet is the birthstone for January. Garnet has a hardness of 6-8 and a specific gravity of 3.5 - 4.3. The formula for garnet is: A3B2(SiO4)3. Pyrope garnet is also called (misleadingly) American Ruby, Arizona Ruby, Australian Ruby, Bohemian Ruby, California Ruby, Cape Ruby, Colorado Ruby, Elie Ruby, Montana Ruby, and Rocky Mountain Ruby.

EnchantedLearning.com
Rock and Mineral Dictionary
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

Click on an underlined word for more information on that subject.
If the rock or mineral term you are looking for is not in the dictionary, please e-mail us and we'll add it.

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