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The tobermorite supergroup; a new nomenclature

Cristian Biagioni, Stefano Merlino and Elena Bonaccorsi
The tobermorite supergroup; a new nomenclature
Mineralogical Magazine (April 2015) 79 (2): 485-495


The name 'tobermorites' includes a number of calcium silicate hydrate (C-S-H) phases differing in their hydration state and sub-cell symmetry. Based on their basal spacing, closely related to the degree of hydration, 14, 11 and 9 Aa compounds have been described. In this paper a new nomenclature scheme for these mineral species is reported. The tobermorite supergroup is defined. It is formed by the tobermorite group and the unclassified minerals plombierite, clinotobermorite and riversideite. Plombierite ('14 Aa tobermorite') is redefined as a crystalline mineral having chemical composition Ca (sub 5) Si (sub 6) O (sub 16) (OH) (sub 2) .7H (sub 2) O. Its type locality is Crestmore, Riverside County, California, USA. The tobermorite group consists of species having a basal spacing of approximately 11 Aa and an orthorhombic sub-cell symmetry. Its general formula is Ca (sub 4+x) (Al (sub y) Si (sub 6-y) )O (sub 15+2x-y) .5H (sub 2) O. Its endmember compositions correspond to tobermorite Ca (sub 5) Si (sub 6) O (sub 17) .5H (sub 2) O (x = 1 and y = 0) and the new species kenotobermorite, Ca (sub 4) Si (sub 6) O (sub 15) (OH) (sub 2) .5H (sub 2) O (x = 0 and y = 0). The type locality of kenotobermorite is the N'Chwaning II mine, Kalahari Manganese Field, South Africa. Within the tobermorite group, tobermorite and kenotobermorite form a complete solid solution. Al-rich samples do not warrant a new name, because Al can only achieve a maximum content of 1/6 of the tetrahedral sites (y = 1). Clinotobermorite, Ca (sub 5) Si (sub 6) O (sub 17) .5H (sub 2) O, is a dimorph of tobermorite having a monoclinic sub-cell symmetry. Finally, the compound with a approximately 9 Aa basal spacing is known as riversideite. Its natural occurrence is not demonstrated unequivocally and its status should be considered as "questionable". The chemical composition of its synthetic counterpart, obtained through partial dehydration of tobermorite, is Ca (sub 5) Si (sub 6) O (sub 16) (OH) (sub 2) . All these mineral species present an order-disorder character and several polytypes are known. This report has been approved by the International Mineralogical Association Commission on New Minerals, Nomenclature and Classification.

ISSN: 0026-461X
EISSN: 1471-8022
Serial Title: Mineralogical Magazine
Serial Volume: 79
Serial Issue: 2
Title: The tobermorite supergroup; a new nomenclature
Affiliation: Universita di Pisa, Dipartimento di Scienze della Terra, Pisa, Italy
Pages: 485-495
Published: 201504
Text Language: English
Publisher: Mineralogical Society, London, United Kingdom
References: 43
Accession Number: 2015-078920
Categories: Mineralogy of silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 3 tables
N33°25'00" - N34°04'60", W117°42'00" - W114°25'00"
Country of Publication: United Kingdom
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, Copyright, Mineralogical Society of Great Britain and Ireland. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201534
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