Coke
Coal + Pyroxene-hornfels facies
Required Geological Setting
Neogene and Quaternary sediments, Paleogene and older sediments + Volcanoes of volcanic island arcs
Occurrence
Coal subjected to pyroxene-hornfels facies contact metamorphism by volcanic rocks intruded in coal beds. Coke is formed by dry-distillation of coal evaporating most volatile components by the heat of intruded dykes such as andesite to dacite. These dykes are called "Don" at coal mines in the northern kyushu island, Japan. Solidification temperature of intruded igneous rocks is estimated 700 - 800 degree, and the peak temperature of contact metamorphism is estimated 670 - 700 degree. There are fissures in coke as the volume of coke is decreased in the dry-distillation process of coal. These fissures are filled with dolomite, calcite, or quartz originated from melt of dykes. Coke bursts with sounds by heating. Coke is classified to a kind of anthracites by the Japanese Industrial Standards (JIS), and defined as its calorific value is higher than 8400 kcal/kg and fuel ratio (Solid-state carbon/volatile component) is higher than 4.0.
Mineral Assemblages
Coke, Calcite, Dolomite, Quartz, Chalcedony