Heulandite
 | This article needs additional citations for verification. (April 2013) |
| Heulandite | ||
|---|---|---|
Mohs scale hardness 3.5–4 | | |
| Lustre | pearly, vitreous | |
| Streak | white | |
| Diaphaneity | transparent to translucent | |
| References | [3][4][5][6] | |
Heulandite is the name of a series of
tectosilicate minerals of the zeolite group. Prior to 1997, heulandite was recognized as a mineral species, but a reclassification in 1997 by the International Mineralogical Association
changed it to a series name, with the mineral species being named:
- Heulandite-Ca
- Heulandite-Na
- Heulandite-K
- Heulandite-Sr
- Heulandite-Ba (described in 2002).
Heulandite-Ca, the most common of these, is a hydrous calcium and aluminium silicate with the formula (Ca,Na)5(Si27Al9)O72·26H2O.[7] Small amounts of sodium and potassium are usually present replacing part of the calcium. Strontium replaces calcium in the heulandite-Sr variety. The appropriate species name depends on the dominant element. The species are visually indistinguishable, and the series name heulandite is still used whenever testing has not been performed.
Crystallography and properties
Crystals are
.The
bisectrix of the optic axes emerges perpendicular to the cleavage.[8]
Suður-Múlasýsla, Iceland
. Clusters of pearlescent, curved heulandite crystals cover the vuggy, thin basalt matrix. Heulandite crystals are up to 2 cm.Discovery and occurrence
Heulandite was first separated from stilbite by
John Henry Heuland (1778–1856).[8]
Heulandite occurs with stilbite and other zeolites in the amygdaloidal cavities of
sedimentary rocks indicates that these have experienced shallow diagenesis.[9]
Good specimens have been found in the basalts of
Sahyadri Mountains of Maharashtra near Mumbai. Crystals of a brick-red colour are from Campsie Fells in Stirlingshire and the Fassa valley in Trentino. A variety known as beaumontite occurs as small yellow crystals on syenitic schist near Baltimore, Maryland.[8]
Notes
- ^ "Heulandite Subgroup". mindat.org. Hudson Institute of Mineralogy. Retrieved 23 February 2025.
- S2CID 235729616.
- ^ Mindat - Heulandite-Ca
- ^ Webmineral - Heulandite-Ca
- ^ Mineralienatlas
- ^ Simon and Schuster's Guide to Rocks and Minerals
- ^ "Heulandite-Ca". mindat.org. Hudson Institute of Mineralogy. Retrieved 23 February 2025.
- ^ a b c d Spencer 1911, p. 416.
- ISBN 0716739054.
References
- Attribution
- This article incorporates text from a publication now in the public domain: Spencer, Leonard James (1911). "Heulandite". In Chisholm, Hugh (ed.). Encyclopædia Britannica. Vol. 13 (11th ed.). Cambridge University Press. p. 416.
External links
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