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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.

B

background extinctions

Background extinctions are those extinctions that occur continually throughout time. These extinctions are caused by small changes in climate or habitat, depleted resources, competition, and other changes that require adaptation and flexibility. Most extinctions (perhaps up to 95 per cent of all extinctions) occur as background extinctions.

Baffa diamond

Baffa diamond is actually rock crystal and not a real diamond.

ballistic fragment

A ballistic fragment is a piece of rock that is ejected from a volcano with great speed.


banded agate

Banded agate is a type of agate with distinct layers of color.

basalt

Basalt is a type of volcanic (igneous) rock. This hard, dark rock is composed of 45 to 54 percent silica (SiO2) and is often rich in iron and magnesium. Basalt is the most common type of rock in the Earth's crust - most of the sea floor is made up of basalt. Basalt forms when lava cools on the surface (whe then same type of lave cools below the surface, gabbro is formed).

basaltic lava

Basaltic lava is a lava composed of molten basalt. This type of lava erupts at temperatures from 1100 to 1250° C. Basalt lava has a low viscosity (resistance to flow); it flows relatively quickly. Shield volcanoes are almost entirely composed of basalt.

base metal

Base metal refers to non-precious metals. Base metals include copper, zinc, tin, and lead.

base surge

A base surge is a cloud of rock debris, water, and steam that moves close to the ground at high speeds. It is formed by an explosive volcanic eruption.

batholith

A batholith is a huge body of igneous rock that solidified under that Earth but now has at least 100 square kilometers (40 square miles) exposed. Half Dome at Yosemite National Park, California, USA, is a granite batholith. Mt. Rushmore was carved from the northeastern edge of the Harney Peak Granite Batholith.
bathymetric map
A bathymetric map is a map of the bottom of a body of water, noting the depth contours (these are called isobaths).

bathypelagic

Bathypelagic means of, pertaining to, or living in the deep ocean near the bottom.


beach glass

Beach glass (also called sea glass) is glass from old broken bottles, windows of wrecked ships, etc. that has been worn down and etched by the sea and sand over the years. This glass is smooth and looks like beautifully sand-blasted glass and has a beautiful patina. Pieces of this glass are collected on beaches. Brown, deep green and clear are the most common colors of sea glass; after these come blue, amber and aqua. Rare colors include pink, red, purple, light yellow, and sea green.

benitoite

Benitoite is a rare, blue gemstone that is found mostly in the San Benito River in San Benito County, near Coalinga, California (lesser quality benitoite is found in Mont St. Hilaire, Quebec, Canada). Benito means "blessed" in Spanish. This gemstones is strongy dichroic; although Benitoite is blue when viewed from most directions, it appears colorless when viewed in a single direction (the c-axis). Some unusual Benitoite is blue, but pink or orange when viewed through the c-axis. Benitoite is BaTiSi3O9 (Barium Titanium Silicate); no one is sure what element causes the blue color of benitoite, but it may be iron. Benitoite has a hardness of 6 - 6.5, a specific gravity of 3.68, and a refractive index of 1.757 - 1.804. Benitoite has a very unusual crystalline shape - it is the only known ditrigonal-dipyramidal crystal. Large stones (over 1 or 2 carats) are exceedingly rare. Benitoite was discovered in California in 1907, either by Mr. Hawkins and T. Edwin Sanders or James Marshall Couch (the story is in dispute). Heat-treated benitoite becomes orange; these stones are more expensive. Benitoite is California's official state gemstone (since 1985).

beryl

Beryls are a family of gemstone that include emerald, aquamarine, beryl (green), red, morganite (yellow), and heliodor (pink). Beryl has a hardness of 7 - 8, a specific gravity of 2.6 - 2.9, and the chemical formula Be3Al2SiO6. Internal flaws in beryl gems can be hidden by treating the stone with oil (this is often not disclosed to the buyer).
Soil Layers diagram
B Horizon

Also called the subsoil - this layer is beneath the E Horizon and above the C Horizon. It contains clay and mineral deposits (like iron, aluminum oxides, and calcium carbonate) that it receives from layers above it when mineralized water drips from the soil above.
1,000,000,000

billion
A billion is a thousand million. Multicellular life evolved on Earth about a billion years ago.

biomass

Biomass is the amount of animal and plant life in an area. Biomass is usually expressed in units of weight per volume.

biota

Biota is the animal and plant life of an area.
birefringence
BIREFRINGENCE

Birefringence is another name for double refraction. In doubly-refractive stones, the light entering the stone is split into two light rays, and the rays travel in different paths. These stones have more than one refractive index. Calcite, peridot, zircon, tourmaline, and titanite are doubly-refractive stones.

BIRTHSTONE

In the 1930's, the British and U.S. jewelry industries assigned stones to the months of the year as follows:
Month Birthstone
January Garnet
February Amethyst
March Aquamarine
April Diamond
May Emerald
June Pearl or Moonstone
July Ruby
August Peridot
September Sapphire
October Opal
November Topaz or Citrine
December Turquoise or Zircon
Black Hills gold ring
Black Hills gold

Black Hills gold is gold jewelry that is made (but not always mined) in the Black Hills area of South Dakota, USA. Gold was first discovered in that area about 1874 by Horatio N. Ross. E.O Lampinen opened the Black Hills Jewelry Manufacturing Company in Deadwood, South Dakota in the early 1900's. Modern day Black Hills jewelry often has a three-color (yellow gold, pink gold and green gold) grape leaf and vine pattern. There are many companies that make Black Hills jewelry today, but by law, their creations must be made from Black Hills gold. This jewelry is often (but not always) 10 Karat gold.


black moonstone

Black moonstone is a type of labradorite and not true moonstone.


black opal

Black opals are a valuable type of precious opals with a dark ground color. They are luminous, iridescent, and frequently have inclusions of many colors ("fire"). Opal is a mineral composed of silica (and some water) and is a species of quartz. The rainbow-like iridescence is caused by tiny crystals of cristobalite. Many opals have a high water content - they can dry out and crack if they are not cared for well (opals should be stored in damp cotton wool). Opals have a hardness of 5.5 to 6.5 and a specific gravity of 1.98-2.50. Black opals are found in Australia.


Black Star diopside
(Black Star of India)

Black star of India is another name for Black Star diopside (CaMgSi2O6), an opaque black gem with a white, four-rayed star (an asterism). It has a hardness of 5.5 and a specific gravity of 3.3 - 3.6. These stones are found mostly in India. Stones are generally cut cabochon and are not enhanced.

block

A volcanic block is a chunk of rock (over 64 mm) that is ejected (thrown) from a volcano. Blocks usually originate from the volcano's cone and are solid chunks of older lava flows. A block is one size of tephra.

bloodstone

Bloodstone (also called heliotrope) is an inexpensive type of chalcedony that is green with red highlights (caused iron oxide). Bloodstone is porous and relatively soft.

blowdown

A blowdown is a area of trees that has been blown over by a volcanic blast.


blue diamond

Blue 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.

bog-oak

Bog-oak is old oak wood that has been blackened and preserved by being in low-oxygen Irish and Scotish peat-bogs for thousands of years. Bog-oak was carved and used as inexpensive Victorian era jewelry. It was also used for decorative objects, bowls, chests, dagger handles, and other decorative items.

Bohemian diamond

A "Bohemian diamond" is not a diamond at all, it is actually a rock crystal.

Bohemian ruby

A Bohemian ruby is actually a pyrope garnet (and not a ruby at all).

bomb, volcanic

A volcanic bomb is a chunk of viscous lava (over 64 mm) that is ejected (thrown) from a volcano. Since they are still viscous when ejected, they often have rounded, aerodynamic shapes. Types of bombs include: breadcrust bombs, ribbon bombs, spindle bombs, spheroidal bombs, and "cow-dung" bombs.

bort

Bort is a term for industrial grade diamonds.

botanical gems

Botanical gems are minerals that form from plants or plant material. Some botanical gems include amber (fossilized tree resin), coconut pearl (a rare, shiny, calcareous, pearl-like mineral that forms inside the coconut, Cocos nucifera), and pearl opal (also called Tabasheer opal, which form in injured bamboo joints).

Braganza

The Braganza is a huge gemstone that may or may not be a diamond. This Portuguese stone is said to weigh 1680 carats (which would make it the largest-known diamond), but it has not been authenticated - it may actually be a clear topaz.

bubbles

Bubbles are spherical or tear-shaped bubbles of gas captured in glass stones. Bubbles can also be found in resins (like plastics and amber), and much less-frequently in minerals (like quartz, emerald, and topaz). Looking for bubbles is one way to determine if a gem is glass or a gemstone.


butte

A butte is a flat-topped rock or hill formation with steep sides.
1,000,000,000


bya
"bya" stands for billions of years ago.

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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