Cob: RE: blue clay

[Baylor, Scott C]

Though most likely not the case, but I thought of this true story when I saw
the blue-clay question:
	
	Gold miners in Virginia City Nevada almost gave up their gold mining
due to an abundance of bothersome Blue Clay in their gold mine in 1859.
Someone had the clay tested and it was discovered that it was silver ore -
worth $2000/ton (1859 dollars).  This became the famous "Comstock Lode' one
of the richest silver finds in history.

	Sounds like clay can be blue for lots of reasons...some of them very
good!

Scott C. Baylor




-----Original Message-----
From: Tim Kring [mailto:tkring at mindspring.com]
Sent: Sunday, April 28, 2002 8:47 AM
To: coblist at deatech.com
Subject: Cob: blue clay


The blue or gray clay is commonly due to reduction of iron in the 
soil.   This is a normal part of soil formation.   ( I am speaking 
primarily of the soils here in Georgia , Ultisols formed in coastal plain 
marine sediments (Where Pat Newberry lives) and Piedmont material forming 
from Granite/ acid crystalline rock formations.   Think of the soil  as 
being a neutral to gray in color to start with.  You could think of it like 
the color of sheet rock.  Because of the  huge amounts of iron (red color) 
and other minerals in the soil, the dirt will have a reddish, brown or 
yellow hue or color.    During saturated periods, the soil microbes (bugs) 
will consume the oxygen out of the soil water.  When this oxygen has been 
used up, they will basically utilize /strip the iron off the soil particles 
or peds themselves.   Once this iron has become mobile due to reduction, it 
washes out  as the water table moves down and out of the soil 
profile.   The soil no longer has its red color which has now been removed, 
the remaining color is the soil color gray or blue.  This is sort of like 
stripping the red wall paper off of the sheet rock.  You can fist see the 
signs of this as you dig down into the ground on a transitional position on 
the landscape,  the deeper you get, the more gray spots or mottles you may 
find depending on how the site is draining.  A lot of water moves laterally 
in the ground not just strait down.  If it didn't, there would be not 
creeks and they certainly wouldn't be flowing during dry periods.    By the 
time you move down the hill or side slope to a creek and or flood plain 
position, the soils may be very gray in and around such bottom land 
areas.  Frequently, you may have to dig down somewhat, due to frequently 
deposited organic matter that is in the surface layers, or depth of water 
table.


Tim in Georgia