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Limestone

		Although dolostone is much more common than limestone in our neighborhood, we sometimes find limestone gravel along railroad tracks and limestone blocks in buildings and steps. To learn more about limestone, scroll farther down this page.
Here's some limestone gravel, collected from a parking lot in Indianapolis, Indiana.

	How to recognize limestone
	Other rocks that look like limestone
	Special things to look for
	Where limestone came from
	How limestone formed
	Other names for limestone
	Links to Web sites about limestone

How to recognize limestone

	Limestone is mostly light to dark gray in color.
	Its grains can be mud-sized, so that the rock looks dull, or they can be sand-sized or larger bits of broken shell or other limey material.
	You can scratch limestone into white powder with a nail or knife. (See more about the scratch test.)
	Limestone is made mostly of the mineral calcite, so it bubbles gently when you put a drop of white vinegar on it.

Other rocks that look like limestone

Dolostone:

Dolostone is made mostly of the mineral, dolomite. It won't bubble in vinegar or acid, unless you scratch off some powder and put the vinegar right on the powder.

White Marble:

	Marble is often a brighter white than limestone.
	Marble's crystals are usually larger than limestone's crystals.
	Like limestone, marble is usually made of calcite, so it usually fizzes gently when you put a drop of white vinegar on it.

Chert: Pieces of chalky white or dark chert are sometimes mixed with limestone gravel.

	Chert is harder -- a nail scratches dolostone, but not chert.
	Chert is smoother -- you may see small or medium-sized crystals in limestone, but not in chert.
	Chert often breaks to form sharp or scalloped edges.

Gray Slag:

	Slag usually has lots of rounded bubble holes.
	If you look closely, you'll see that slag is often somewhat glassy in spots (especially inside bubble holes).
	Some spots bubble in vinegar or acid, but most places do not.

Where limestone came from

We're not sure where the limestone gravel that we
find in our neighborhood came from.

How limestone formed

Most limestones in our part of the world formed in
shallow seas that covered our area hundreds of
millions of years ago.

Other names for limestone

We use the scientific name "limestone" for this rock,
but it is also known by many other names:

When limestone is crushed into gravel and
used for building roads or making concrete, it's often called an aggregate.

Here are some ways to classify limestone (by grouping it with similar types of rocks):

	Geologists have a catch-all term that includes both limestone and dolostone. They call them carbonate rocks.
	Limestone is a sedimentary rock.

Links to Web sites about limestone

This Volcano World page has some information about limestone.
< http://volcano.und.nodak.edu/vwdocs/vwlessons/lessons/Slideshow/Serocks/Sedrock6.html >

The Indiana Limestone Institute of America's Web site has
information about the most common limestone building stone
in our area.
< http://www.iliai.com/ >

Here's an article about underground limestone mining in Iowa.
< http://www.igsb.uiowa.edu/browse/undrlime/undrlime.htm >

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This page was created on October 14, 2001, and it was last updated on July 27, 2002.