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Clays and Clay Minerals

, Volume 21, Issue 2, pp 103–114 | Cite as

The Crystal Structure of Talc

  • J. H. Rayner
  • G. Brown
Article

Abstract

The crystal structure of a sample of talc from Harford County, Maryland, has been determined by least squares refinement from X-ray diffraction photographs. A triclinic cell with a = 5·293, b = 9·179, c = 9·496Å, α = 90·57°, β = 98·91°, γ = 90·03, space group C1̄ is adopted. The layers of the structure have almost monoclinic symmetry but the nearly hexagonal rings of oxygen atoms on the surfaces of the layers, formed by the bases of the silica tetrahedra, are not held in register by interlayer ions as they are in micas but are partly displaced so that the stack of layers forms a triclinic crystal. The hexagons of surface oxygens are distorted by a 3·4° twist of the tetrahedra so that the b axis is 0·2 per cent shorter than in a structure with regular hexagons, and the twist brings the oxygen ions a little closer to the octahedral magnesium ions.

Résumé

La structure cristalline d’un échantillon de talc du Harford County, Maryland, a été déterminée par un raffinement par moindres carrés à partir de clichés photographiques de diffraction des rayons X. On a adopté une maille triclinique de groups C1̄, avec a = 5,293 Å, b = 9,179 Å, c = 9,496 Å, α = 90,57°, β = 98,91° et γ = 90,03°.

Les couches de la structure ont presque une symétrie monoclinique, mais les anneaux d’atomes d’oxygène de surface, d’une forme voisine de l’hexagone, formés par les bases des tétraèdres de silice ne sont pas en correspondance exacte comme ils le sont dans les micas où se trouvent des ions interfeuillets; ils sont au contraire déplacés en partie, si bien que l’empilement des feuillets forme un cristal triclinique. Les hexagones des atomes d’oxygène de surface sont déformés à cause d’une rotation des tétraèdes de 3,4°; ainsi l’axe b est plus court de 0,2% de ce qu’il est dans une structure à hexagones réguliers, et la rotation des tétraèdres rapproche un petit peu les ions oxygène des ions magnésium octaédriques.

Kurzreferat

Die Kristallstruktur einer Talkprobe aus Harford County, Maryland, wurde aus Röntgenbeugungsaufnahmen unter Berechnung der kleinsten Abweichungsquadrate bestimmt. Es wurde eine trikline Zelle mit a = 5,293, b = 9,179, c = 9,496 Å, α = 90,57°, β = 98,91° und γ = 90,03°, Raumgruppe C1 angenommen. Die Schichten dieser Struktur haben fast monokline Symmetrie, doch werden die nahezu hexagonalen Ringe der Sauerstoffatome an den durch die Grundflächen der Si-Tetraeder gebildeten Schichtoberflächen nicht durch Zwischenschichtionen aufeinander ausgerichtet, wie dies bei den Glimmern der Fall ist. Sie sind vielmehr teilweise versetzt, so daß die Schichtfolge einen triklinen Kristall bildet. Die Sechsecke der Oberflächensauerstoffe sind durch eine 3,4°-Drehung der Tetraeder verzerrt, so daß die b-Achse um 0,2% kürzer ist als in einer Struktur mit regelmäßigen Sechsecken. Die Drehung bringt die Sauerstoffionen etwas näher an die oktaedrischen Magnesiumionen heran.

Резюме

Структура кристаллов талька определялась при помощи рентгенографии по образцу из харфордского округа, Мэриланд. Принята триклинная клетка с a = 5,293, b = 9,179, с = 9,496 Å, α = 90,57°, β = 98,91°, γ = 90,03, промежуток группы С 1. Слои структуры имеют почти что моноклинную симметрию, но на поверхности слоев имеются примерно шестигранные кольца атомов кислорода, которые не содержатся в равновесии в межслойных ионах как в слюде, а частично смещены, так что столбик слоя образует триклинный кристалл. Шестигранники поверхностных кислородов искажены скручиванием тетраэдры на 3,4°, таким образом ось b на 0,2 % короче, чем структура с регулярными шестигранниками, а скручивание слегка приближает ионы кислорода к октаэдральным ионам магния.

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Copyright information

© Clay Minerals Society 1973

Authors and Affiliations

  • J. H. Rayner
    • 1
  • G. Brown
    • 1
  1. 1.Pedology DepartmentRothamsted Experimental StationHarpenden, HertsEngland

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