Limestone Types for Dummies

One limestone classification

Our staffers get pretty good at recognizing the names of frequent contributors, which is why they were already familiar with Leaf Group "cleanup team" member Laurie Brenner (Reeves) when they encountered the Sciencing.com article "Name Five Different Types of Limestone." What they found interesting, however, is Laurie's newly-crafted bio, which claims she has a "[deep] interest in science." Huh: over at HomeSteady, she's called herself a "contractor"...

Be that as it may, Reeves (making her sixth appearance as a DotD, her first in science) started out with a problem. When she did the teardown on the previous version of her rewrite, written by Kelly Smith, she found a list of five: lime, chalk, coral reefs, travertine, and "limestone for construction." We agree with Reeves that Kelly's list was... well, bullshit. We do not, however, think Laurie did much better. After all, she started out wrong-footed by explaining that,

"As a sedimentary rock mostly composed of calcite, calcium carbonate and the shells and exoskeletons of marine life, many different variations of limestone occur in nature..."

Umm, Laurie? calcite and calcium carbonate are the same thing! So, let's see Laurie's list:

"Chalk: The famous White Cliffs of Dover consist of chalk, a type of limestone. The skeletons of small algae called coccoliths, deposited over thousands of years, became the white mud chalk that made the cliffs." Coral Reef Limestone: "Coral reefs provide examples of limestone made from the skeletons of coral invertebrate – animals that do not have backbones – in the ocean and even on dry land. " "Animal Shell Limestone: Besides coral reef limestone, other animal shell limestone includes crinoidal and fusilinid limestone." "Limestone Variety – Travertine: As a compressed type of limestone, travertine forms along streams, near waterfalls and around hot or cold springs that are active for tens of thousands of years." "Black Limestone Rock: ... If you find a dark gray to black limestone rock, it gets its color from the organic materials fused within it..."

Our geologist (whose MS is in sedimentology, the study of sedimentary rocks) had some corrections for Laurie:

1. The alga is a coccolithophore; a coccolith is a fragment of the little guy. I'd also be more inclined to say millions, not thousands of years.
2. That reads like coral reefs form on dry land. They don't. That's not to mention that a coral reef fits neatly into the next classification...
3. Oh, crap, Laurie: there are thousands of different kinds of coquina, the technical name for a limestone composed mostly of shells. I've seen fossiliferous limestone featuring clams, snails, brachiopods, bryozoans, trilobites, horn corals, ammonites... 
4. No, Laurie, not "along streams," unless the stream is running from the mouth of a mineral spring. And I have no earthly idea what you mean by "compressed type of limestone"!
5. As far as I know, "Black Limestone Rock" is not a type of limestone, since any of the types you've already mentioned can be organic-rich (except the travertine).

Clearly, Laurie was struggling for a fifth type. Maybe she should have tried oolitic? lithographic?

Apparently, Brenner's interest in picking up even more freelancing dollars by performing rewrites exceeds the depth of her interest in scientific accuracy; thereby earning her yet another Dumbass of the Day award for her (lack of) effort.

copyright © 2019-2022 scmrak

SI - PETROLOGY