Beryl and Tourmaline
Barbour Pit, Stoneham, Maine

The specimen shown here is a 38 cm. long, curving crystal of beryl on a 20 cm. wide base of feldspar, quartz, and schorl tourmaline. It was found at the Barbour Pit in Stoneham, Maine. Although the long crystal has been repaired in several places, it is still visually dramatic. The specimen was acquired by the Museum in 1993 from Jim Mann.

Beryl Be₃Al₂Si₆O₁₈

Cyclosilicates; Beryllium aluminum silicate, frequently with some sodium, lithium, and cesium

Color and Luster: Bright green(Var. emerald), blue, greenish-blue(Var. aquamarine), yellow(Var. golden beryl), red, pink(Var. morganite), white, colorless; vitreous; streak colorless

Hardness: 7.5-8

Cleavage: Indistinct, one direction

Fracture: Uneven to concoidal

Crystals: Hexagonal; crystals common, usually six-sided prisms that are striated lengthwise

Hexagonal, prismatic crystals occur most commonly as a major component in late stage igneous rocks known as pegmatites and is mined as the chief source of the element beryllium. Crystals of beryl have been found in Maine up to 20 and 30 meters in length and weighing several thousand kilograms.

Tourmaline group Na(Mg,Fe)₃Al₆(BO₃)₃(Si₆O₁₈)(OH,F)₄

Cyclosilicates; complex silicate of boron and aluminum, whose composition varies widely because of substitutions

Color and Luster: Black(Var. schorl), blue(Var. indicolite), pink and red(Var. rubellite), brown(Var. dravite), green, multicolored, rarely white; vitreous, streak white

Hardness: 7-7.5

Cleavage: None

Fracture: Uneven, conchoidal

Crystals: Hexagonal, usually short to long prismatic crystals that commonly have a rounded triangular cross section, striated lengthwise; also radiating, columnar, compact

Photo by Mary Sutherland

Descriptions taken from
The Audubon Society Field Guide to North American Rocks and Minerals