TERMIUM Plus®

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SUB-SILICIC ROCK [1 record]

Record 1 2011-05-06

English

Subject field(s)
  • Petrography
  • Geochemistry
DEF

An igneous rock having a relatively low silica content, sometimes delimited arbitrarily as 44% to 51% or 45% to 52%.

CONT

Igneous rocks [are subdivided] into the following groups: silicic or felsic (or acid, an old and discredited but unfortunately entrenched term), rocks having more than 66 percent silica; intermediate, rocks with 55 to 66 percent silica; and subsilicic, rocks containing less than 55 percent silica. The latter may be further divided into two groups: mafic, rocks with 45 to 55 percent ...

OBS

"Basic" is one of four subdivisions of a widely used system for classifying igneous rocks based on their silica content: acidic, intermediate, basic, and ultrabasic.

OBS

The term "subsilicic rock" is preferred to "basic rock" (the most commonly used term) which is misleading.

OBS

"Basic" must not be confused with "alkaline."

Key term(s)
  • sub-silicic rock

French

Domaine(s)
  • Pétrographie
  • Géochimie
CONT

L'acidité d'une roche est liée à sa teneur en silice, [...] les roches dites basiques en contiennent environ 50 %.

CONT

[...] un très grand nombre de dépôts cuprifères, aurifères, cobaltifères, nickélifères, et argentifères se localisent dans des roches basiques [...]

OBS

La notion d'acidité, quelque peu ambiguë pour les roches, a été introduite au milieu du siècle dernier par Élie de Beaumont qui, en fonction de la teneur en SiO2, distingue les roches acides [plus de 65 %], les roches intermédiaires [entre 52 et 65 %], les roches basiques [entre 45 et 52 %] et les roches ultra-basiques [moins de 45 %].

Spanish

Campo(s) temático(s)
  • Petrografía
  • Geoquímica
DEF

Roca que posee menos de un 60% de SiO2 y en la que no hay sílice libre, sino que toda forma parte de silicatos.

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