Limestone Island in Phang Nga Bay
Islands of Phang Nga Bay

The island of Phang Nga Bay started life underwater 130 million years ago as part of the largest coral reef in the world. The coral reef stretched from the Malay Border to the North of Vietnam. The coral grew and died forming a deposit of CALCITE or CALCIUM CARBONATE hundredsof metres thick. This formed the basis of LlMESTONE - the main rock inthe islands.

75 million years ago, the limestone was pushed upwards form the sea bed by the pressure of the movements of the worlds plates. This is a similar effect to the formation of mountains.

The islands we see have been shaped by the effec.ts of wind, rain, wave and current action over the past 75 million years.

Limestone is sedimentary rock. About 8%  of the earth's surface is sedimentary ,rock. Fossils are a distinguishing tfeature of sedimentary rock. However, fossilscan be found In other types of rocks too. Non-marine origin limestone occurs due to diagenesis ("dia" is Greek for "throughII."Genesis" is Greek for beginning or origin). Sediments are deposited initially as unconsolidated debris. Consolidation comes about gradually due to dewatering (not in the type of limestone in Phang Nga Bay) and / or because of cementing with a binding material (clay, calcium, lime). The rock is altered and gradually changes into limestone through this process called diagenesis. Rocks that have become solid in this way are described by ending with the word "stone". Like, limestone, mudstone, and sandstone. Almost all sedimentary rock is layered. Reef limestone is generally not layered.

They develop as an atoll or frinsing reef. Lime is continuously deposited by the coral animal (polyps ).

Pure limestone is snow white. Other colors are caused by other rocks:  
  * Limonite and siderite cause yellow-brown shades
  * Hematite causes red    
  * Glauconite and chlorite cause green     
  * Bitumen causes gray to black     

 Limestone of marine origin

This limestone is a monomineralic (one mineral) rock consisting of a single
mineral (calcite) which can mak up 95% of the rock. Other_rocks found in marine limestone include dolomite, si erite, quartz, feldspar, mica, and various clay materials.

Fragments from the hard parts of marine animals and plants, the parts which contain calcium, form the sediment. The main sources of calcium come from algae, corals, calcareous sponges, foraminiferids (certain plankton), bryozoa (moss animals) ,brachiopods (lampshells) , echinoderms (starfish, sea urchins, sea cucumbers, sealilies) , mollusks (snails, bivalves, chitons, octopus, squid) , crustacea (barnacles,lobsters, crabs, shrimp) , and pteropods (some snails, sea slugs, abalone, cowries,limpets ).

When they die, they leave behind either complete units or skeletons. Sometimes the former organism is recognizrble (fossils ). Other times, it is completely broken down.

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