Distinction of dolomites based on texturein the Middle Jurassic carhnnate rocksof Northeast Mashhad

The Mozduran One Formation (Middle Jura~!;ic ) in NE Ma!;hhad is mainly composed o f dolomite and limestone. Based on texture (size and fabri c), dolomites were divided into 5 diITerent types with a crystal size which ranges from 10 to 1200 microns. Type one is very fine tn fine subhedral to euhedral crystals. while type two is fine to medium euhedral with poikilotopic texture. Type three is medium planar suhhedralto anhedral crystals with idintopic texture. Type four is medium to coarse anhedral nonpianar crystals and type five is coarse with dolomite cement. Distinction between types 3 and ,1 is difficuil and is mainly based on the larger number of crystal hthliidries in type three and stronger undulose extinction in type four. Dolomite.chr('39')I of types nne to three are mainly formed in the early stages. while types 4 and 5 formed during the burial. in the late stages of the diagenetic history of the rock. It is concluded that bachr('39')led on texture. dolomites can be divided into different types and thereby the ir origin can be interpreted.