การเกิด
A snorkeler gliding above a reef sees an incredibly diverse community of coral and algae, around which creatures such as clams, oysters, snails (gastropods), and lampshells (brachiopods) live, and above which plankton float (a figure above). Though they look so different from each other, many of these organisms share an important characteristic: they make solid shells of calcium carbonate (CaCO3). The CaCO3 crystallizes either as calcite or aragonite. (These minerals have the same composition, but different crystal structures.) When the organisms die, the shells remain and may accumulate.
Rocks formed dominantly from this material are the biochemical version of limestone. Since the principal compound making up limestone is CaCO3, geologists refer to limestone as a type of carbonate rock. Limestone comes in a variety of textures, because the material that forms it accumulates in a variety of ways. For example, limestone can originate from reef builders (such as coral) that grew in place, from shell debris that was broken up and transported, from carbonate mud, or from plankton shells that settled like snow out of water. Because of this variety, geologists distinguish among fossiliferous limestone, consisting of visible fossil shells or shell fragments (b figure above); micrite, consisting of very fine carbonate mud; and chalk, consisting of plankton shells. Experts recognize many other types as well. Typically, limestone is a massive light-gray to darkbluish-gray rock that breaks into chunky blocks it doesn't look much like a pile of shell fragments (c figure above). That’s because several processes change the texture of the rock over time. For example, water passing through the rock not only precipitates cement but also dissolves some carbonate grains and causes new ones to grow.
การเกิด(Snorkeler)กลุ่มที่ร่อนอยู่เหนือแนวปะการังเห็นเป็นชุมชนที่มีความหลากหลายอย่างเหลือเชื่อของปะการังและสาหร่าย รอบซึ่งสิ่งมีชีวิตเช่นหอย นางรม หอยทาก (gastropods), และ lampshells (น้ำด้วยอวัยวะ) สด และแพลงก์ตอนซึ่ง float (ตัวเลขข้างต้น) แม้ว่าพวกเขามีลักษณะแตกต่างจากคนอื่น ๆ หลายของสิ่งมีชีวิตเหล่านี้ใช้ร่วมกันคุณลักษณะสำคัญ: พวกเขาทำให้เปลือกแข็งของแคลเซียมคาร์บอเนต (CaCO3) CaCO3 ตก เป็นแคลไซต์หรือแร่อะ (แร่ธาตุเหล่านี้มีองค์ประกอบเดียว แต่โครงสร้างผลึกแตกต่างกัน) เมื่อสิ่งมีชีวิตที่ตาย เปลือกหอยยังคงอยู่ และอาจสะสม Rocks formed dominantly from this material are the biochemical version of limestone. Since the principal compound making up limestone is CaCO3, geologists refer to limestone as a type of carbonate rock. Limestone comes in a variety of textures, because the material that forms it accumulates in a variety of ways. For example, limestone can originate from reef builders (such as coral) that grew in place, from shell debris that was broken up and transported, from carbonate mud, or from plankton shells that settled like snow out of water. Because of this variety, geologists distinguish among fossiliferous limestone, consisting of visible fossil shells or shell fragments (b figure above); micrite, consisting of very fine carbonate mud; and chalk, consisting of plankton shells. Experts recognize many other types as well. Typically, limestone is a massive light-gray to darkbluish-gray rock that breaks into chunky blocks it doesn't look much like a pile of shell fragments (c figure above). That’s because several processes change the texture of the rock over time. For example, water passing through the rock not only precipitates cement but also dissolves some carbonate grains and causes new ones to grow.
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