Genesa Batugamping Merah Muda Di Daerah Klepu, Kecamatan Kokap, Kabupaten Kulon Progo, Yogyakarta

ABSTRAK The existence of pink and white limestones which are scattered sporadically at Klepu area of Kokap sub-district in Kulon Progo Regency, Special Teritory of Yogyakarta (DIY) is geologically interesting to be explained with respect to their genetic, due to invariably colors white and grayish white. The limestone is one of the other members of Jonggrangan Formation. To explain genetically why the limestone is pink, it is necessary to analyse ,the petrographical, chemical, and normative mineralogical compositions. Stratigraphical information of the area is helpful in this study. Based on this study it is concluded that the existence of titanoferous magnetite with its FeO.Fe203.Ti02 chemical formula and red in color has caused the limestone to acquire the pink color. It has been figured out that the mineral was derived from "Old Andesite Formation" which bears FeO, Fe203, and TiO2 chemical composition. The stratigraphical information which support of the interpretation is the "Old Andesite Formation" has unconformity relation with and older than pink limestone, so when the limestone began to be deposited mechanically, titanoferous magnetite which was from the "Old Andesite Formation" entered into the limestone depositional environment. This process influenced limestone composition and resulted a part of the limestone has pink color syngenetically

Characteristics and genesis of montmorilonitic claystone from Bandung area, Wonosegoro, Boyolali, Central Java, Indonesia

The Bandung bentonite deposit is located in Wonosegoro District, Boyolali Regence, Central Java. Characteristics of bentonite in this area are very important due to increase demand on bentonite in the industry. Several methods are used to characterize the bentonite in this area, such as PLM (polarizing light microscope), X-Ray Diffraction and Scanning Electron Microscope combined with EDX measurements. The montmorilonitic claystone belongs to Kerek Formation from Banyuurip Member. This deposit consists of mainly montmorilonitic claystone interbedded with tuffaceous sandstone. Petrographical analysis shows that montmorilonitic claystone consists of mostly clay minerals with small amount of calcite, volcanic glass, feldspar, quartz, and opaque minerals. The clay minerals are likely as alteration product of volcanic glass. The oriented XRD analyses show that the clay samples consist of Ca-montmorilonite, illite, and kaolinite. Physico-chemical analyses of montmorilonitic claystone display that the initial CEC (cation exchange capacity) is 20 mgrek.Na2O/200gr (54 mg.Na2O/100gr) and low swelling ability for about 2 times of its initial volume. Based on its mineralogical association, textures, and stratigraphic position, the montmorilonite is formed from devitivication of volcanic glass in a diagenetic environment with over 2 km thicks of overburden. Keywords: Bentonite, montmorillonitic claystone, devitrivication, diagenesis, montmorillonit

CHARACTERISTICS AND GENESIS OF MONTMORILONITIC CLAYSTONE FROM BANDUNG AREA, WONOSEGORO, BOYOLALI, CENTRAL JAVA, INDONESIA

The Bandung bentonite deposit is located in Wonosegoro District, Boyolali Regence, Central Java. Characteristics of bentonite in this area are very important due to increase demand on bentonite in the industry. Several methods are used to characterize the bentonite in this area, such as PLM (polarizing light microscope), X- Ray Diffraction and Scanning Electron Microscope combined with EDX measurements. The montmorilonitic claystone belongs to Kerek Formation from Banyuurip Member. This deposit consists of mainly montmorilonitic claystone interbedded with tuffaceous sandstone. Petrographical analysis shows that montmorilonitic claystone consists of mostly clay minerals with small amount of calcite, volcanic glass, feldspar, quartz, and opaque minerals. The clay minerals are likely as alteration product of volcanic glass. The oriented XRD analyses show that the clay samples consist of Ca-montmorilonite, illite, and kaolinite. Physico-chemical analyses of montmorilonitic claystone display that the initial CEC (cation exchange capacity) is 20 mgrek.Na2O/200gr (54 mg.Na2O/100gr) and low swelling ability for about 2 times of its initial volume. Based on its mineralogical association, textures, and stratigraphic position, the montmorilonite is formed from devitivication of volcanic glass in a diagenetic environment with over 2 km thicks of overburden.</p