Limestone/Sandstone

["Dr. Tim Palmer" <tjp@xxxxxxxxxx>]

Hi Anthony,

The criteria that you mention below are not enough.
Many limestones have sedimentary layering, and some
sandstones lack it (though absence of layering combined
with a dense creamy consistency is often a marker for
limestones.

We geologists use three testing methods.  The first is
to put a drop of dilute Hydrochloric acid on the surface
and see if it fizzes.  This is a good test for the
mineral calcite (calcium carbonate) of which most
limestones are made.  Beware, though; some sandstones
contain a natural calcite cement.  They will fizz like a
limestone.

Or look closely with a x10 magnifier.  Often the quartz
grains of a sandstone will be clearly visible as greyish
or brownish, slightly translucent grains.

But the best way by far, and the one that distinguishes
the true stone-lover from the fastidious dilettante <:)>
is to scrape a minute flake of the stone off a fresh
clean surface and to nibble it between the front teeth.
Limestones are slightly crunchy but soon break down into
a smooth paste.  The quartz grains in a sandstone are
much harder and will take much more of a bite to crush
them.  Sometimes they will even squeak a bit as you
chew.  Do a comparison once between a known sandstone
and a known limestone and you will immediately
experience the difference.

Of course there is no guarantee that bits of tooth edge
will not occasionally spall off (only on sandstones:
never on limestones), but most geologists over here in
England have no worse teeth than non-geological
Englishmen...

Tim

At 13:27 28/03/00 -0500, you wrote: