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Thread: Travertine and Limestone for once and for all

  1. #1
    Wicked SRN Membah!! DUSTY's Avatar
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    Travertine and Limestone for once and for all

    Straight out of the Geology book

    To understand Travertine - you first need to know what Tufa, and dripstone are.

    Tufas are caclite deposits that build up around the rim of calcite rich springs. Tufa often builds towers underwater where springs bubble up in to lakes or under the sea. Although Tufas are chemical rocks, algae and other plant material does play a part in their formation. Algae actively spurs tufa to precipitate, forming algal mats or mounds called stromatolites made of tufa bound together by filaments of algae. Often the algae rots away leaving a sponge like rock called sinter. tufa is sometimes called calcareous sinter to distinguish from siliceous sinter, a sinter that forms by precipitation of opaline silica. Because it is so full of holes, tufa is light and easy to cut, which is why the romans used it to line the aqua appia, the underground aqueduct they built in 312bc to supply Rome with water.


    Travertine:
    Tufa forms mainly around cool springs, typically when plants take carbon dioxide from the water and make less available to combine with calcium. Around hot springs, calcite is precipitated when hot water loses carbon dioxide as it cools. This leaves dense hard crusts, such as those around Mammoth Hot Springs in Yellowstone. The terms Tufa and Travertine are sometimes used interchangeably, but geologists usually call the dense variety travertine, and the spongy variety Tufa.


    Dripstone:
    Although most travertines form around hot springs, the most beautiful and spectacular are often those that form in limestone caverns. Here calcite rich waters dripping from the ceiling create deposits called dripstones. dripstones can build up into stalactites hanging from the ceiling - or stalagmites projecting from the floor. Sliced across these dripstones reveal how they were built up in layers, darker and lighter bands.
    cavern walls and floors contunually wet with running water may be coated in sheets of travertine called flowstone.



    Limestone:

    Limestones are almost entirely the work of living things. Huge sea beds of limestone thousands of meters thick may be the accumulated remains of countless sea creatures piled up on the sea bed over millions of years, then slowly changed to rock as theirchemistry alters. Living things contribute to the creation of limestone in two ways. sometimes they contribute their skeletal remains, their hard shells and bones, to the rock. Alternatively ,like plankton and algae, they change the chemistry of the sea, and encourage the deposit of calcite. the key chemicals in limestone are carbonates - and in particular calcium carbonate in the form of calcite or argonite. carbonate sediments may be rich in either calcite or argonite, but ancient limestones are almost always calcite rich because argonite alters over time to calcite.
    Limestones form in many places - soils on old rocks, river flood plains, lakes - but most are the creation of shallow clear tropical waters. Here there is not only an abundance of sea life, but evaporation of such warm waters boosts the precipitation of calcium carbonates. This does not mean that limestones are found only in the tropics, however. the continents have shifted so much through the ages that many places now nearer the arctic were once in the tropics. During the carboniferous period around 300 million years ago, much of what is now North America, and Europe lay in the tropics, and was inundated by vast tropical seas. Huge beds of limestone, now visible in places such as Texas and the English Pennines, are the legacy of this time.In England such limestones are called Carboniferous Limestones.




    To summarize:

    Travertine - chemical stone formed by hot springs or dripping calcite

    Limestone - accumulated dead sea animals whose chemistry changed over years plus calcium carbonate.
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  2. #2
    SRN Member Dave K's Avatar
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    Very informative. So really porus travertine is Tufas, meduim or low porus travertine is travertine and dense or non porus, layered travertine is flowstone, Cool. If we give credit to the geology book we could blog this.

    There is also limestone in New England. About 10 minutes from me is a limestone mine.

    Thanks Dusty

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    Wicked SRN Membah!! DUSTY's Avatar
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    Yeh there's plenty of limestone in the states. The fabby I used to work for actually has the exclusive rights to sell Green River Stone in new england. Awesome history - we cut it into counters, but mostly they sell gallery type pieces - awesome stuff. Smelled like oil when we cut it

    Some enormous Tortoise'ssss pom frons and fish. From Wyoming amazing how this world has shifted.

    http://www.greenriverstone.com/about/company/
    Friends Don't Let Friends Buy Engineered Stone

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    SRN Member Dave K's Avatar
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    Cool stuff. It must be nerve racking to detail something like a turtle fossil.

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