Friday Rock Blogging: Caliche

a pebble partially coated with calcite I’ve previously rockblogged about the crusty, water-soluble minerals known as evaporites. But you don’t need open pans or puddles to produce this kind of mineral precipitate – drying out shallow soil will work just as well. When this happens, dissolved calcium carbonates (et al.) will coat all kinds of surfaces and infiltrate all kinds of voids within the soil, from pebbles (shown here) and fractures to partly buried tree trunks. Often, repeated cycles of wetting and drying will produce a layer of evaporated gunk that cements the soil grains together just a few inches below the surface; this layer is commonly known as hardpan, or caliche. The crusty gunk itself is also called caliche; though some people reserve the term for calcium carbonates, others don’t care. Calcite is the commonest precipitate anyway. Then there are the people in India who call it kankar, which just makes me giggle.

One of the virtues of caliche is that it keeps a record of the kinds of chemical isotopes present in the water it came from. In an article in this week’s Science, Prosenjit Ghosh et al. use the isotopic record from old caliche nodules in Bolivia to deduce the uplift history of the Altiplano (or “eastern Andes” if you want). They claim that the Altiplano rose fast, about 1 mm/yr over a period of 4 million years, which is of tremendous interest to those of us who get paid to think about mountains. But since it’s seminar time, I’ll just leave it as… hardpan: not quite so shitty as gardeners would have you believe.

Comments

  1. Ruth wrote:

    I thought all I needed to know about caliche is that it is danged hard to dig through, and makes gardening in Santa Fe nearly impossible.

  2. delagar wrote:

    Yay!

  3. Modulator wrote:

    Friday Ark #71
    We’ll post links to sites that have Friday (plus or minus a few days) photos of their chosen animals (photoshops at our discretion and humans only in supporting roles). Watch the Exception category for rocks, beer, coffee cups, and….? We will add yo…

  4. Dr. Pattanowski wrote:

    Rocks and fossils may be the keys to understanding the past but with evaporites one may rub the past all over themselves. Tomorrow, my wife and daughter shall go to a cliffside shelter to play in the Lower St.Louis limestone anhydrites. We are just sure to keep the dust level down.

  5. Devin Bent wrote:

    Does breathing caliche dust cause health problems? Are there relevant EPA standards. (I know that the posts above date from 6 years ago, but I’m hoping someone will answer.)

    I’d be grateful for any assistance.

  6. Maria wrote:

    Breathing any dust can cause health problems but I doubt caliche dust is special. There are EPA standards for particulate matter, I’d try those.

  7. Devin Bent wrote:

    Thanks,

    I have read on another site that there are EPA standards, but perhaps they are for people who work with/in caliche.

    Also, IMO, there seem to be major differences in dust. In some homes I’ve read that it can be as much aa 90% human skin.

    Thanks again.

    Devin

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