Bixbyite,
Rutile, and
Amethyst Crystals near Marysvale, Piute County
Geologic information:
The Marysvale area is dominated by Tertiary igneous rocks ranging from
intermediate to silicic compositions with both volcanic and plutonic
representatives. The especially thick volcanic section is thought to be
the result of a large stratovolcano complex and associated calderas that
existed during mid-Tertiary time.
One of the common units found near Marysvale is a
white to dark gray rhyolite with extremely well-developed flow banding.
The crystals, which are found in cavities in the rhyolite, formed in gas
pockets that were trapped in the lava flow as it cooled.
Bixbyite, a rare iron-manganese oxide, occurs as
black, metallic, euhedral crystals up to 3/8 of an inch across. The
crystals are generally complex combinations of various isometric forms
including cubes, octahedrons, and dodecahedrons.
Rutile is less common and appears as needle-like or
bladed crystals up to 1/4 inch long.
The amethyst crystals, ranging up to 1 inch in
length, display excellent crystal form in various shades of purple.
The small size of the bixbyite and rutile is more
than compensated for by the excellent crystal forms of these relatively
rare minerals.
How to get there: Travel 2.8 miles north on
Center Street in Marysvale on US Route 89. As you begin to enter Sevier
Canyon, look for an unmarked gravel road (exactly at 2.8 miles) and turn
left (west). Continue approximately 300 hundred yards where you can park
alongside the gravel road.
Where to collect: The rhyolite unit does not
crop out within viewing distance of the collecting site. The area along
the gravel road is a gently sloping field with a small dry wash running
through it. Boulders and cobbles of the rhyolite unit are scattered
everywhere in the field and many good samples can be found just by careful
examination of cavities in the rhyolite.
Look for lighter colored pieces of rhyolite with a
porous texture of abundant cavities and break them with a large hammer. Be
careful as the rhyolite is hard and fragments are sharp. The best samples
are found by carefully prying open the cavities in the smaller, broken
pieces.
Useful maps: Beaver and Richfield
1:100,000-scale metric topographic maps, and a Utah highway map are best
for navigational purposes. The Marysvale 1:24,000-scale topographic map
may also be useful.
Land ownership: Bureau of Land Management
(BLM)
public lands.
BLM collecting rules: The casual collector
may take small amounts of gemstones and rocks from unrestricted federal
lands in Utah without obtaining a special permit if collection is for
personal, noncommercial purposes. Collection in large quantities or for
commercial purposes requires a permit, lease, or license from the BLM.
Miscellaneous: A hat and water are
recommended, as are the following tools: safety glasses, a five-pound or
larger sledge hammer, chisel, and newspaper or other suitable wrapping
material. Have fun collecting!
About the author: Stanley C. Hatfield is a
geology professor at Southern Utah University where he teaches a variety
of topics including mineralogy, igneous petrology, and metallic mineral
deposits. Originally from Ohio, he has taught in Utah for over five years.
Much of his free time is spent collecting rocks and minerals and
conducting field trips throughout southern Utah.
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