**5. Petrographic examination**

Thirty-five thin-section slides are carefully studied to identify the mineralogical assemblages of the Kolosh sandstones. The modal analysis and average percentages are shown in **Table 1**. Petrographic identification of various mineralogical constituents is followed [21–28].

Olivine group: varieties of olivine minerals are identified, such as fayalite, forsterite, monticellite, and chondrodite, with an average percentage of 8.3% (Pl/1 A-E). They are mostly prismatic, angular to subangular, and are less common than pyroxene. Most olivine grains are fresh and few grains are uralitized and others have iron oxides and serpentine along the fractures.

Pyroxene group: Clino and orthopyroxenes are recognized based essentially on the extinction angle and petrographic properties. The average percentage of pyroxene minerals is 18.26%.


#### **Table 1.**

*The average percentages of the mineralogical constituent in the studied sandstones of the Kolosh formation in Badelyan locality.*

Clinopyroxene is of hedenbergite, aegirine-augite, diopside, spodumene, pigeonite, and jadeite minerals. These grains are mostly fine and angular to subangular and of prismatic shape (Pl/1 F and H, Pl/2 A-D). Most of the clinopyroxene grains are fresh and others are altered to iron oxide or uralite in the center and a rim of pyroxene is still fresh (Pl/3 G).

Orthopyroxene: hypersthene and enstatite are recognized (Pl/1 G, Pl/2 D), mostly prismatic, angular to subangular, fresh with few altered grains. Orthopyroxenes are less common than clinopyroxene grains.

Feldspar group: plagioclase and alkali-feldspars are identified such as Ca-plagioclase as major type mainly of anorthite and minor bytownite and labradorite composition. The alkali-feldspar is anorthoclase and sanidine (Pl/4 A-D). Feldspar grains are mostly prismatic, fine, angular to subangular and have about 6.17% altogether. Some grains show sericite or carbonate replacement but keep the original shape.

Quartz attains average percentage of 2.05% of total grains, and has fine and subangular to subrounded shape (Pl/4 F).

Cristobalite attains average of 0.51%, less than quartz grains and is fine, angular to subangular grains (Pl/4 E).

Rock fragments: various types are recognized mostly igneous types with subordinate sedimentary and rare metamorphic fragments. The types of igneous fragments are ultrabasic, basic and few acidic, and intrusive and extrusive grains. While the types of sedimentary fragments are argillaceous, chert, chalcedony, and carbonate grains. The average percentage of various types of rock fragments is 15–20%.

Igneous rock fragments of intrusive and extrusive types, are composed of mainly ultrabasic, basic, and subordinate acidic fragments, attaining average of about 11.35%, these are:


*Abnormal Ophiolite (Olivine/Pyroxene Rich) Sandstone NE Iraq: An Approach to the Origin… DOI: http://dx.doi.org/10.5772/intechopen.108333*


The classification of sandstone cf. [13] and [14] provenance and tectonic setting diagram cannot applicate due to the high content of olivine, pyroxene, ultrabasic and basic, and altered fragments, which reach more than 50%.
