Keywords : Petrography

Mineralogy, Petrography and Chemistry of Two Local Plasters, Iraq

Ibraheem R. Baddi; Zeki A. Aljubouri

Iraqi National Journal of Earth Sciences, 2012, Volume 12, Issue 2, Pages 1-16

The mineralogy, petrography and chemistry of two local plasters
(Rasheed and Madae'n) and a dental stone were studied. Mineralogical study
by x-ray diffraction spectrometer proved that the three gypsum products consist mainly of bassanite or hemihydrate (CaSO4. 0.5 H2O) with minor amounts of gypsum and anhydrite. The petrography of the studied thin sections, reveals that the two local plasters consist of dispersed prismatic, monoclinic crystals with
ill-defined edges (bassanite of the β-hemihydrate). Dental stone consists of more packed, prismatic monoclinic crystals with well-defined and sharp edges
(bassanite of the α–hemihydrate). Compressed powders of the two local plasters improved their crystal shapes and edges and made their outlines similar to dental stone or (α–hemihydrate).
Chemical analyses of Rasheed and Madae'n plasters suggest that they consist of more than (96%) bassanite with small amounts of gypsum and anhydrite. Based on these compositions, the two local plasters are suitable for moulding, casting and constructional purposes. They are unsuitable for surgical plasters.

Petrography and Diagentic Processes in Sandstone of Injana Formation in Kand Fold, North Iraq

Mohammed A. AL-Rashedi Thamer A. Aghwan

Iraqi National Journal of Earth Sciences, 2006, Volume 6, Issue 2, Pages 11-24

The sandstone of Injana Formation (Late Miocene) in Kand anticline consists dominently of carbonate rock fragments, among other types, followed by quartz, feldspars and mica. The ground mass is represented by higher amount of calcite cement in comparison to silica, clay and ferrigenous cements.
Classification of the sandstones indicates their calclithic litharenite type. The source rocks embrace sedimentary, metamorphic and igneous rocks.
The sandstones have been affected by early-diagentic events which mainly include carbonate cement and consequently subduced compaction. The processes of early-mesogentic diagenesis resulted in a decrease of primary porosity with a concomittant increase of secondary porosity during late diagenetic stage due to dissolution of carbonate cement.

Petrography and Mineralogy of Jabal Sanam Gypsum Rocks, Southern Iraq

Basim H. Soltan Abdul-Aziz M. Al-Hamdani Abdul-mutalib H. Al-marsoumi

Iraqi National Journal of Earth Sciences, 2005, Volume 5, Issue 1, Pages 18-29

Jabal Sanam is a salt plug, with cap rocks characterized by the presence of evaporitic sequence, where gypsum forms large part of this sequence. The field observations showed that gypsum occurs in form of massive beds and veins, In addition four petrological types of gypsum are recognized; alabastrine, selenite, fibrous, and rocky gypsum. The examination of (61) thin sections besides the X-ray analyses proved that the available gypsum represents the dominant mineral with few to trace amount of anhydrite, dolomite and quartz. Petrographically, four types of gypsum textures are also identified; alabastrine, porphyroblastic, fibrous and granular. All these textures suggest a secondary origin of Jabal Sanam gypsum due to the hydration of pre-existing anhydrite. The hydration occurs when the cap rocks approach the ground surface. The connate and groundwater form the main source of hydration water.