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.     
Red plume agate has been made famous by the
Woodward Ranch, (432) 364-2271 as
they offer agate collecting for a fee south of Alpine, TX.  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