Agate
Gemstone of the Big Bend
                          By Paul Graybeal
      West Texas is famous for its wide variety of unique and beautiful agates and
jaspers. Some types are highly prized by collectors world wide.  35 million years
ago, volcanic activity in the Big Bend produced the environment for our beautiful
gemstones. Quartz crystallizing as nodules inside gas pockets, or in cracks to
form vein type agate, delicate plumes, bands, moss or bouquet patterns of
different colors are actually crystals of impurities such as iron oxide, other oxides,
hematite, etc.  Agate and chalcedony is widespread throughout  this region,  but
only a small amount is of lapidary interest.  Agate has been found south of Sierra
Blanca, all the way down the Rio Grande, past Del Rio.  I would expect many
unique varieties to be found  throughout the Big Bend region in isolated pockets,
as well as all the agate that was carried down the Rio Grande to form fluvial
deposits.  Texas has no public lands to collect on, so there is still a lot to explore
if permission can be obtained.     
      Terri Smith in Alpine also offers field trips to the Walker ranch for a fee.  She
can be reached at (432) 837-3881 at the Antelope Lodge. There are several
types of agate besides red plume to be found on the Woodward Ranch, as well  
on other ranches close by. Black and brown plume being the most common
lapidary grade. Banded agate is fairly common in West Texas,  near Alpine it is
usually white, nearly clear, but can be shades of red, purple or pink, often
surrounding a plume.  Yellow plume can be found, typically with much sugar,
(euhedral quartz) sometimes making it difficult to cut.  There is orbicular agate
found south of Alpine called peanut agate which can be quite beautiful.  Mostly of
it a solid orange color inside the orbs, but peanut agate can also be formed of
independent orbs of different colored bands and small plumes in other orbs in the
same stone.  This type is difficult to cut as not all the orbs are always cemented
together, or some orbs may contain small geodes.                         
   Most of the lapidary grade agate found south of Alpine is found in biscuit
shaped nodules with a dark red skin.  All most all types of agate found in this lava
flow can be found in these biscuits.  About 10% will have a gemstone quality to
them, or only 10% of the stone will have something worth the labour to cut.  It is
rare a stone is full of a red/black plume, gem grade orbicular or colored bands.  
Many of the biscuits did not fill the entire gas pocket, and had space to crystallize
in a shape with bubbles, or botryoidal crystal.  Most agate with this type of form
has plume inside the bubbles.  Most  true biscuits shaped agates  have some
euhedral quartz inside them, and some open up to become true geodes.  Flower
garden agate is formed in cracks in the host rock, making it a vein type
formation.  Usually orange and red, made up of small dense microscopic plumes
is found in isolated pockets.  This type should be considered as jasper as you
cannot see through it, and I have seen other locations such as in Mexico and
Arizona that have similar deposits of flower garden.
   Marfa Texas has some of the most beautiful agate in the world, In my opinion,
though it does not seem that the best quality is very common in  the agate beds I
have been allowed to collect in.  Made famous by Andy Burgard in the 1940s,
pastel colors in "bouquet" patterns are the most sought after by collectors. Marfa
is host to huge agate fields,  all around us are beds of large white and clear
agates, (chalcedony) but few agate beds seem to contain much of the colored
material known as "bouquet".  Most common in lapidary grade is a black plume or
black and yellow plume agate.  It can be in a vary clear agate, or in a  white
fortification agate, often times calcite is included.   Bouquet pattern can be found
with black plume in both white skin and black skin agate,as well as with all other
types of agate found in this geological formation.  Most of the bouquet is a tan,
orange or yellow color, red and purple colors are quite rare for Marfa.  White skin
is usually clear background, black skin nodules can be dark or white banding
background.  The bouquet pattern is usually on the bottom, but can form on the
entire surface and point towards the center in small clusters.  A lot of this agate
is egg shell,  thin coating of agate lining the gas pocket, often with the botryoidal
crystals.  This usually is a good sign of quality plumes or bouquet.  Black skin egg
shell typically is black or blue and white banding.  In one location the black skin
type is a tubes type agate, looking like stalactites inside some of the eggshell
nodules.
   Another famous location of agate in the Big Bend is needle peak, south of
Terlingua. The Woodward ranch conducts tours there for green moss and
pompom agate.  Beautiful pseudomorphs have been found here.  Again there are
many grades of agate, and some nice agate replacement in wood and bone in
the area.
   Balmorhea is famous for their blue agate, banded often with black plumes.  
The skin is usually black with a white patina on the surface.  It appears to be
fairly wide spread in isolated pockets northwest of the Davis Mountains.  The
Blue Agate Rock and Gift shop in Fort Davis has a nice collection
(432.426.2924).  The Davis mountains has little agate I'm aware of, but does
have a lot of chalcedony roses.  To the East of the Davis Mountains are deposits
of agate, though not much of interest to serious collectors that I'm aware of.   I
have seen pretty flower garden from the Sierra Blanca area.    
   There are many theories about agate formation. Some suggest a silicon gel, or
silicon dissolved as a colloidal solution which saturates the host rock. Quartz is
water soluble at high temperatures, so as it cools It forms inside veins, gas
pockets, or can replace other minerals as pseudo morph, or fossils such as
wood, bone and coral.  No one theory explains all types of agate, and some like
our "peanut agate" has no theory at all that I have read about.
Alpine Texas red and black plume agate
Some nice Marfa
rough agate
Alpine Texas red & black agate
Marfa bouquet agate with black skin
Red plume agate
Alpine
Marfa Bouquet
black skin
Pink bands in lava
Bouquet agate slabs
Marfa blue and black banded agate
Big Bend
Fortification agates
Marfa blue agate
black skin
Pompom agate
Terlingua
Terlingua Texas pom pom agate
Pompom
Terlingua
Marfa Bouquet
white skin
Terlingua texas thistle agate
Thistle agate
Terlingua
Marfa tube
agate
Orbicular agate
Shafter, Tx
Peanut agate
Alpine
Marfa
bouquet
white skin
Marfa
bouquet
white skin
faces
Flower
Garden
jasper,
Pom Pom
Needle
Peak
Marfa
bouquet
white skin
old collection
Marfa bouquet
black skin
old collection
Marfa
bouquet
old
collection
Marfa black
plume
white bands
Marfa agate rough
Alpine Texas red agate