Let
us cut your very own geode!
Be the first to see inside One of Mother
Nature's most spectacular and fascinating creations: Geodes.
You'll never know what you'll find when this volcanic gas
bubble, millions of years old, is opened for the very first
time.
Geodes
101
A geode is an unusual, rounded mineral formation typically
with an exterior shell of chalcedony (very fine-grained
quartz), with other minerals and / or crystals lining the
interior. The name geode is from the Greek geo referring
to the shape of the earth, since most geodes are spherical.
A geode can form in
any cavity within a rock, but the most common method for
geode formation is via gas bubbles that form in cooling
ash beds. The bubble gets “frozen” in place
when the silica rich ash / dust hardens. The partial or
complete filling of the bubble may occur immediately or
even thousands to millions of years later and can encompass
a variety of different minerals.
Geodes can also be
filled with surrounding silt and sediments, forming a “mud
ball.” If a crystal breaks off inside the geode, you
can hear rattling (the only guarantee of a hollow geode!),
hence the nickname “rattlestone”. Occasionally,
water gets trapped in the geodes, forming what is called
an enhydro, Greek for “water inside”.
We’ve nicknamed
geodes Mother Nature’s lottery ticket, as you never
know what you’ll have until we cut it open. Geodes
are fascinating and unique forms of nature, and like fingerprints,
no two are exactly alike!
Dugway
6
to 8 million years ago, volcanic activity in Western Utah
deposited an igneous rock called rhyolite. Trapped gases
formed pockets in the rhyolite, which eventually became
lined with chalcedony and quartz from groundwater. Most
Dugways fluoresce a lime green color due to minute amounts
of a secondary mineral that bonded with the quartz when
it was growing. 32,000 to 14,000 years ago, a large lake
covered most of Western Utah. The lakes wave activity eroded
the rhyolite and actually moved the geodes several miles
away to their current location in Juab County, Utah.
Choyas
Choyas
geodes are mined in a 44 million year old volcanic deposit
in an area of Chihuahua, Mexico called Las Choyas. Nicknamed
“coconut geodes” because of their roundness
and size, Choyas are literally hand dug with a pickaxe out
of a tough bentonite clay. Miners fill potato sacks with
the geodes and raise them up narrow shafts from 75 to 125
feet beneath the surface! Composed mainly of any variety
of quartz, including the ever popular amethyst, Choyas are
especially fascinating because of the wide variety of secondary
minerals found in them.
Septarian
Septarian
geodes formed 100 million years ago when the Gulf of Mexico
reached up to southern Utah. When sea life died, it became
trapped in sediments and formed mud balls. As the sea receded,
the mud balls dried and cracked in the sun. The sea returned,
and calcium from newly decomposing shells eventually seeped
into the cracks and recrystallized as calcite (yellow.)
The thin brown wall is aragonite and the gray exterior is
bentonite clay. The name Septarium comes from the Latin
“septum”, meaning dividing wall.
Brazilian
Brazilian
geodes are worked in a large open pit mining operation in
Rio Grande de Sol, Brazil. These geodes are filled with
beautiful layers of banded agate that form under relatively
low temperatures of 45-54°F and pressures. A striking
feature of the agate is the occurrence of dendritic inclusions
resembling trees, bushes or even sunbursts, caused by a
mineral growth of manganese oxide.
Thunder
Egg
Thunder
Egg geodes formed in volcanic ash tuffs in the Pacific Northwest
20 million years ago. These remarkable geodes have a beautiful
star shaped pattern of chalcedony with colored agate filling
the middle. The name Thunder Egg originates from an old
Indian legend that states two angry gods located on neighboring
mountains got into a violent fight and used eggs taken from
the nest of thunderbirds as weapons. After the fight, the
“weapons” were found scattered on the ground.
