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Rock and Mineral Dictionary
An ice age is a time lasting thousands of years during which the Earth is very cold and largely covered by ice and glaciers.
An igneous intrusion (also called a laccolith or a plutonic formation) 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).
When molten rock cools, igneous rock is formed. Intrusive rocks are igneous rocks that have formed (and cooled slowly) beneath the surface of the Earth. Extrusive rocks are igneous rocks that have formed (and cooled more quickly) at the surface of the Earth (like obsidian). Some igneous rocks include granite, obsidian (volcanic glass), basalt, and andesite porphyry.
Impact craters are the remains of collisions between an asteroid or meteorite and the Earth.
Imperial jade is another name for emerald jade. It is a fine emerald-green color.
Imperial topaz is golden orange-yellow topaz; it is the most valuable type of topaz.
Imperial Mexican jade
Imperial Mexican jade is not jade at all; it is calcite that has been dyed green.
Inca emerald is an emerald that is mined in Equador.
An inclusion is a particle of foreign matter contained within a mineral. Inclusions can be solid, liquid, or gaseous. Many inclusions decrease the value of a stone, but some, like rutile forming asterisms in star sapphires and needles in rutilated quartz and tourmalinated quartz, are prized.
Index fossils are commonly found fossils that are limited in time span. They help in dating other fossils. For example: trilobites were common during the Paleozoic, but not found before the Permian period, and ammonites were common during the Mesozoic Era, but not found after the Cretaceous period.
Indian agate is another term for moss agate.
Indicolite is a green to blue-green variety of tourmaline.
Intergrown crystals occur when two mineral crystals grow together and become one.
intrusive igneous rock
Intrusive rocks are igneous rocks that have formed (and cooled slowly) beneath the surface of the Earth. These rocks usually have a coarse-grained or medium-grained texture, like granite.
Inverall sapphires are a type of sapphire from Inverall, New South Wales.
Iolite (meaning 'violet stone'), also known as water sapphire and lynx sapphire, is a transparent, violet-blue, light blue, or yellow-gray mineral. Iolite is pleochroic; a single stone will show many colors (in the case of Iolite, violet-blue, light blue, and yellow-gray). Iolite is not rare and has a hardness of 7 - 7.5. Iolite is found in Sri Lanka, India, Madagascar and Burma.
An ion is an atom that is missing one or more electrons; ions have an electrical charge.
An iridescent object displays many lustrous, changing colors. Iridescence is caused by the reflection of light from the jewel.
Iridium is a metal related to platinum. Iridium and platinum are frequently alloyed together, since the iridium increases the workability of the platinum. Iridium is also used for the points of gold-nibbed pens.
Iridium is an element that is rare on the Earth's surface, but abundant on chondritic meteors. The presence of excess Iridium at the K-T layer (the Iridium anomaly) supports the Alvarez asteroid theory.
Irish diamond is not a diamond at all; it is rock crystal from Ireland.
Iron is a metal. Its mineral forms include pyrite and marcasite).
Irradiation is the act of being exposed to radiation. Many stones (like kunzite) are irradiated in order to enhance their color. Being irradiated changes the crystal structure of the mineral by moving electrons. Irradiation techniques bombard the crystal with high-energy radiation (like gamma rays), producing a stone with very little radioactivity and a change of color. Some color changes caused by Irradiation are permanent, others care unstable and be reversed by heating or exposure to sunlight. For example, colorless topaz changes to a cinnamon brown color after ibeing irradiated with cobalt-60 radiation, but the color fades as the stone is exposed to sunlight. A new method of irradiation changes clear topaz to a brilliant, non-fading blue.
An isotope of an element is another form of the same element, that has a different number of neutrons in the nucleus (giving it a different atomic weight).
Italian lapis is not lapis; it is actually blue-dyed jasper from Italy.
Rock and Mineral Dictionary
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