Bicol region had the third biggest shale reserves in the 1990s.
Rocks as sources of natural gas? Today’s Discover Geology series introduces you to shale, a fine-grained sedimentary rock formed through the deposition and compaction of silts and clays.
Shale is the most abundant type of sedimentary rock categorized under mudstone. They account for 70% of the earth’s crust. Shales are laminated, which means they are made up of thin layers, and fissile, meaning they readily split into thin pieces.
Shales are commonly black and grey; however, some are yellow, red, brown, or green. The black or grey color indicates the presence of organic materials. Those that are formed on environments with deposits of hematite, goethite, or limonite produce red, brown or yellow shale. Meanwhile, clay minerals and micas, typically greenish, make up the green shales.
Did you know that we use shale in the petroleum industry? Black shales are the source of oil and natural gas formed during the deposition and burial of organic materials. Shale gas is mainly composed of methane. Some of these shale gas deposits formed during the Devonian period or 300-400 million years ago.
Shale is also used in making blocks of cement. The calcium oxide from crushed limestone is mixed with a heated shale. This sedimentary rock is an essential component in bricks, tiles, and pottery.
Meanwhile, the Bicol region had the third biggest shale reserves in the 1990s, according to the Department of Environment and Natural Resources (DENR). The Ragay Hills, which lies on the southwest side of the Bicol River, consists of folded and faulted sedimentary rock formations, including shale.
The National Museum of the Philippines Bicol is under repair and remains closed.