study of some features of the oolitic and pisolitic ironstones bin the hussainiyat formation ( middle jurasic), westren desert of iraq

Oolites and pisolites of the ironstones in the hussainiyat formation (middle Jurassic) are common deposits in the western desert of Iraq. They are composed of three main types; 1-hematitic oolites and pisolites with out defined concentric layers 2- goethitic oolites and pisoolites with well defined layer and 3 oolites and pisolites partly hematitic and partly goethitic. Most of the oolites and pisolites have well spherical shapes, whereas, few of hematitic pisolites have an egg-shapes. They also have floating contacts, but others with concavo convex, points and rather long contacts. The internal structure and mineral features indicate that most of these oolites and pisolite are of iron origin, and not to be altered from calcitic one. The hematitic position within the oolites and pisolites may indicate that these are older than the goethitic ones. The longitudinal, concavo-convex contact probably produced from the transportation rather than the compaction effect, where as, the sutured, convex and point contacts between quartz grains in the matrix are probably originated by the compaction effect.