Hello Andrew D.,

The Alabama coastline is short but somewhat varied. The shoreline east of
the mouth of Mobile Bay has nearly pure quartz sand and, on a good day, is
literally as white and blinding as snow. This shoreline is nearly continuous
with that of Pensacola, Florida. On the seacoast near Pensacola, the water
is nearly clear. (N.B.: White sand, unlike glass, reflects ultraviolet
light. My mother once wrapped herself up for a safe nap on the sand, but the
light that reflected onto the soles of her feet burned them.)

West of Mobile Bay on the Alabama-Mississippi coast, the sand is also nearly
pure quartz, but is not as clean due to the muddiness of the water. But the
Mobile River basin (which includes the Alabama, Tombigbee, and Coosa Rivers)
delivers such a heavy load of mud that Mobile Bay is one of the muddiest
along the Gulf Coast. The water is in the bay itself carries so much mud
that one's hand becomes invisible when immersed only a few inches. This
muddy water is delivered to Mississippi Sound and to the Gulf of Mexico, and
tends to travel to the west with the longshore current.

The very muddy Mississippi River currently delivers turbid water to the Gulf
mainly at its mouth and through a controlled channel into Atchafalaya Bay,
Louisiana. Other areas have been largely leveed off, so the old flow
patterns have been changed. In its natural state, muddy Mississippi
floodwater could reach the mouth of Mobile Bay. At present, this could still
happen if the Bonne Carre spillway were opened to carry water into Lake
Ponchartrain, Louisiana. But in normal years, the bulk of Mississippi mud is
carried westward from its mouths, not north toward Alabama.

Black streaks do occur in the sand, comprising less than one percent of it
by weight. These are composed of dark, dense minerals that are relatively
resistant to weathering, as quartz is. The minerals include iron and
titanium compounds such as magnetite, ilmenite, and rutile; magnetite of
course is magnetic and can be collected by stroking a magnet along the
surface of dry black sand.

You can consider the beach sand -- and all that clay too -- and the entire
apron of deposits that we call the Coastal Plain -- to be ultimately the
result of the gradual breakdown of the Appalachian Mountains. The black sand
tends to be finer-grained than the quartz sand. This is because the waves
and currents have a maximum weight that they can carry, and the black sand
is denser than the quartz sand. Given time, the water sorts the sand out
according to size and density.

You may also see windrows of muddy, greenish pellets that smear when walked
on. These are the cylindrical fecal pellets of ghost shrimp, so called
because they are pale and rarely leave their burrows. The shrimp feed on
turbid water and actually clean the water by filtering it. The pellets are
composed mainly of clay and don't smell although they are enriched in
organic matter. They are a favorite food of mullet, and it has been
hypothesized that they are full of fermenting microbes that make them more
nutritious. Because of their clay composition, which doesn't rot, they are
sometimes fossilized and even used as index fossils to gauge the age of
strata. It's a bizarre world we live in, no doubt about that.

Andrew K. Rindsberg
Geological Survey of Alabama

Quick guide to pronunciation:

Atchafalaya = a-CHAHF-a-LYE-a
Biloxi = Bi-LUCK-see
Dauphin [Island] = DAW-fin
Mobile = Mo-BEEL
Pontchartain = PONCH-a-train, unless you're a French-speaker, in which case
it's Ponh-shar-trenh with "nh" indicating nasal vowels.

As Walt Kelly said, "Pensacola, it's the spot!"

+++++++++++++++++

Hi,
The sand off the Gulf Coast of Alabama is white.
I was just in Mississippi area and sand is light but not as white as
Alabama.

Marion Deuel

Andrew Dickson wrote:

> Dear Conchlers,
>
> Scaphella junonia johnstonae has a brown base color.  Could this be
> caused by certain sediments mixed with the sand and mud which were washed
> into the Gulf of Mexico by the Mississippi River?  I have never been to
> this region of the U.S.  What color is the sand off the Alabama /
> Mississippi area?
>
> Andrew
> [log in to unmask]