대톨라이트(Datolite)

Loc: Verchniy Quarry, Dal'negorsk, Primorskiy Kray, C.I.S., Russia

단사정계(單斜晶系)의 규산염광물이다. 굳기는 5~5.5, 비중은 3이고, 백색, 담녹색, 적색, 황색을 띤다. 염기성 화성암의 맥 또는 틈 속에서 2차광물로 산출되고 방해석, 제올라이트 등과 함께 있기도 한다.

화학성분은 CaB［SiO4］(OH)이다. 단주상(短柱狀) 결정을 이루지만, 때로는 포도상 ·단괴상(團塊狀)을 이루기도 한다. 굳기 5∼5.5, 비중 3이다. 백색 ·담녹색 ·적색 ·황색을 띠며, 파란 형광을 발하는 것이 많지만, 박편(薄片)에서는 무색이다. 흔히 염기성 화성암의 맥이나 틈 속에 2차광물로서 산출되며, 방해석 ·제올라이트 등과 함께 있는 경우도 많다.

•Chemistry: CaBSiO4(OH), Calcium Boron Silicate Hydroxide.

•Class: Silicates

•Subclass: Nesosilicates

•Group: Datolite

•Uses: As a mineral specimen, rarely as an ornamental stone and as a minor gemstone.

Three individual Datolite crystals rise above the quartz and calcite base of this specimen. The largest of these has dimensions of 2.3 x 1.0 x 0.9" (5.8 x 2.5 x 2.3 cm), and the others are less than half that size. They occur as rather thick monoclinic prismatic crystals that have a pearly luster, and they have a pale green color and are transparent and moderately clear in some areas, though they contain many internal fractures and flaws. There is only a very small amount of visible damage to the crystals, which are all at least partially coated with a thin druse of tiny, intergrown, clear quartz crystals. The base on which the Datolites rest is made up of several clear, hexagonal prismatic quartz crystals that have a matte luster and many shards of calcite that represent broken, bladed crystals.

Datolite is a popular mineral among mineral collectors although it is somewhat obscure. It forms nicely faceted complex crystals. The crystals at first glance could appear to be other crystal forms such as the isometric dodecahedron or trapezohedron. However these highly symmetric crystal forms are easily distinguished from the crystals of datolite. Datolite's crystals although usually well formed and strickingly faceted lack any symmetry elements except for one mirror plane and one axis of two fold rotation.

Datolite is often found in basalt vesicles with calcite and zeolites. In fact, it is often confused with certain zeolites because of its luster, color and associations. Datolite is also found in the Lake Superior region of Michigan. It is associated with native copper at this location and is found in porcelain-like masses and nodules. The nodules are brown to off white in color and some are cut and polished as a ornamental stone.

PHYSICAL CHARACTERISTICS:

•Color is white, colorless, yellowish, reddish, gray, brown and green.

•Luster is vitreous to greasy.

•Transparency: Crystals are transparent to translucent.

•Crystal System: Monoclinic; 2/m

•Crystal Habits include short prismatic to wedge shaped tabular crystals with complex and richly faceted terminations. Also in porcelain-like masses that form nodules. Aggregates can be fibrous or granular.

•Cleavage is absent.

•Fracture is conchoidal to uneven.

•Hardness is 5 - 5.5

•Specific Gravity is 2.8 - 3.0

•Streak is white.

•Associated Minerals are prehnite, danburite, babingtonite, epidote, copper, calcite, quartz and zeolites.

•Notable Occurances include Russia; Lake Superior region of Michigan and Paterson, New Jersey, USA; Bancroft, Ontario, Canada; Charcas, Mexico; Schwarzwald, Germany and Norway.

•Best Field Indicators are crystal habit, absence of cleavage, hardness and color.