Petrography and Mineralogy of Gercus and Fat'ha Formations Gypsum: A Comparative Study

The petrography and mineralogy of the gypsums from the Gercus
(Lower Eocene) and Fat'ha (Middle Miocene) formations were
investigated. Petrographically, the gypsums of both formations
consist of two main textures: porphyroblastic of minimal extent
and alabastrine of very wide distribution. Alabastrine texture could
be divided according to shape, size and outlines of crystals into
three hydration stages. The first stage texture consists of composite
crystals and feathery texture, where in the Fat'ha Formation, they
have about equal distribution of this stage and (87%) of the first
and second hydration stages. The third Stage is absent from the
gypsum of the Fat'ha Formation. Feathery texture is absent from
gypsum of the Gercus Formation, and the composite crystals of
stage one make up only about 12% of the three stages, except in
the massive gypsum of Duhok Dam, where they make up 50%. Xray diffraction study revealed that massive gypsum of Duhok Dam
(Gercus Formation) and nodular gypsum of Baashiqa area (Fat'ha
Formation) have very similar intensities for the three secondary
characteristic peaks at d-spacings of (4.27 Ǻ, 3.79 Ǻ and 3.06
respectively and higher than that of nodular gypsum of Duhok
Dam and Zawita junction (Gercus Formation). The presence of
relatively large proportions of composite crystals in massive
gypsum of Duhok Dam and nodular gypsum