Casey inspects a piece of common Opal while Allen
whacks away at a big chunk.
Jane Henry keeps a watchful eye while Ron Francis
and grandson Cameron move a rather large specimen of Opal along
the rails.
If only the Chinese Camp gas station were still open
– what a great price!
Red
Hills Magnesite
By Jenni Long
On Saturday, February
7th, several MLMS members joined a COOP field trip to the Red
Hills of Tuolumne County. Most of us were very unfamiliar with
one of the materials we were to collect, Magnesite. We were told
it had been mined in these hills near Chinese Camp quite some
time ago but the mine was abandoned and now opened for collecting.
So, what exactly could
we do with our collected Magnesite? With a hardness of 3.5 -
5 on the Moh's Scale, it could be cut and polished and the harder
specimens possibly tumbled. Once cut and polished the Magnesite
resembles white turquoise. In fact, "the most common imitation
of turquoise encountered today is dyed howlite and Magnesite."
Magnesite's black veining makes it the most convincing "stand-in"
for turquoise, once dyed the familiar blue color.
Magnesite has uses other
than ornamental. It is the primary ore for magnesium and can
be found in certain types of cement, paper and rubber. It also
has uses in nutritional supplements (magnesium oxide).
How is Magnesite formed?
The most widely accepted theory is that carbon dioxide-charged
surface waters percolated down through fissures in serpentine.
The magnesium silicates of the serpentine were then changed into
magnesium carbonate. This makes perfect sense after being on
location … there was serpentine everywhere! In fact this
particular location is right in the middle of what's known as
the "Sierra Nevada metamorphic belt," where one of
the largest exposures of serpentine rocks exists.
Back to the Chinese Camp
location, according to the Bureau of Land Management, several
hundred tons of crude Magnesite ore were mined from the 1860s
to the 1940s with most of the production occurring in the 1920s.
Rumor has it, large quantities of the Magnesite made it over
to China where it was cut, dyed and then sent back to the United
States to be sold as imitation turquoise! So, how can you "test"
your turquoise to make sure it's not Magnesite in disguise? Magnesite
will dissolve in hot hydrochloric acid. But, if you don't happen
to have some spare hydrochloric acid lying around, use your tongue!
Because of micro-pores on the surface, your tongue will adhere
to the porcelaneous material . . . mmm, tastes like chicken!
