Natrolite in the context of "Mineral"

Acicular, in mineralogy, refers to a crystal habit composed of slender, needle-like crystals. Crystals with this habit tend to be fragile. Complete, undamaged acicular specimens are uncommon.

The term "acicular" derives from the Late Latin "acicula" meaning "little needle". Strictly speaking, the word refers to a growth habit that is slender and tapering to a point. Prismatic crystals are not acicular; however, colloquial usage has altered the commonly understood meaning of the word. When writing for mineralogical publications, authors should restrict their usage of "acicular" to crystals with the tapering growth habit.

Boehmite or böhmite is an aluminium oxide hydroxide (γ-AlO(OH)) mineral, a component of the aluminium ore bauxite. It is dimorphous with diaspore. It crystallizes in the orthorhombic dipyramidal system and is typically massive in habit. It is white with tints of yellow, green, brown or red due to impurities. It has a vitreous to pearly luster, a Mohs hardness of 3 to 3.5 and a specific gravity of 3.00 to 3.07. It is colorless in thin section, optically biaxial positive with refractive indices of nα = 1.644 – 1.648, nβ = 1.654 – 1.657 and nγ = 1.661 – 1.668.

Boehmite occurs in tropical laterites and bauxites developed on alumino-silicate bedrock. It also occurs as a hydrothermal alteration product of corundum and nepheline. It occurs with kaolinite, gibbsite and diaspore in bauxite deposits; and with nepheline, gibbsite, diaspore, natrolite and analcime in nepheline pegmatites. Industrially, it is used as an inexpensive flame retardant additive for fire-safe polymers.

Hohentwiel (German pronunciation: [ˈhoːənˌtviːl] ) is a mountain of volcanic origin in the Hegau region of Baden-Württemberg in southern Germany. It is the Hausberg of the industrial city of Singen, located west of it and ca 10 km (6.2 mi) west of Zeller See (Lake Constance). The ruins of the medieval Hohentwiel Castle rest on top of it.

Hohentwiel was an active volcano about 7–8 million years ago during the Miocene epoch, along with several other volcanoes in the Hegau region. It mostly consists of phonolite, which represents the former volcanic pipe. The surrounding softer rocks have been eroded over time by ice age glaciers during the Riss glaciation, creating an inverted relief and giving the mountain its present-day shape.

Mesolite is a tectosilicate mineral with formula Na₂Ca₂Si₉Al₆O₃₀·8H₂O. It is a member of the zeolite group and the natrolite subgroup, also resembling natrolite in appearance.

Mesolite crystallizes in the orthorhombic system and typically forms fibrous, acicular prismatic crystals or masses. Radiating sprays of needlelike crystals are not uncommon. It is vitreous in luster and clear to white in color. It has a Mohs hardness of 5 to 5.5 and a low specific gravity of 2.2 to 2.4. The refractive indices are nα=1.505 nβ=1.505 nγ=1.506.

Gonnardite is a comparatively rare, fibrous zeolite, natrolite subgroup. Older papers claim that a complete solid solution exists between tetranatrolite and gonnardite, but tetranatrolite was discredited as a separate species in 1999. A series, based on the disorder of the silicon-aluminum in the framework, appears to exist between Na-rich gonnardite and natrolite, Na₂(Si₃Al₂)O₁₀·2H₂O.

Gonnardite was named in 1896 after Ferdinand Pierre Joseph Gonnard (1833–1923), who was Professor of Mining Engineering at the University of Lyon, France.