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three-sided or six-sided prisms terminated by rhombohedral or scalenohedral planes. Black tourmaline (schorl) is the most common variety, but there are also other varieties, as the blue (indicolite), red (rubellite), also green, brown, and white. The red and green varieties when transparent are valued as jewels. [Writt…

diamond in hardness and other properties. It occurs in nature also in boracite, datolite, tourmaline, and some other minerals. Atomic weight 10.9. Symbol B.

A double salt of boric and silicic acids, as in the natural minerals tourmaline, datolite, etc.

nd peridot. Sometimes used as a gem. The name was also early used for yellow varieties of tourmaline and topaz.

The mineral black tourmaline or schorl; -- so called by the Cornish miners. Raymond.

A variety of tourmaline of an indigo-blue color.

ite from Luxullian, Cornwall, characterized by the presence of radiating groups of minute tourmaline crystals.

and polarizes the light. It is usually a reflecting plate, or a plate of some crystal, as tourmaline, or a doubly refracting crystal.

ed to negative crystal, or one in which this characteristic is reversed, as Iceland spar, tourmaline, etc. -- Positive degree (Gram.), that state of an adjective or adverb which denotes simple quality, without comparison or relation to increase or diminution; as, wise, noble. -- Positive electricity (Elec), the kind…

A variety of tourmaline varying in color from a pale rose to a deep ruby, and containing lithium.

to quartz when containing acicular crystals of other minerals, most commonly rutile, also tourmaline, actinolite, and the like.

Black tourmaline. [Written also shorl.]

See Tourmaline.