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
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.
Some nice Marfa
Red plume agate
Pink bands in lava
Bouquet agate slabs
Marfa blue agate