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GEOLOGY ARTICLE
Cleaning quartz
an excerpt from "Collecting Crystals" by Mike and
Darcy Howard
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How to start
06.21.00--Now that you have collected some nice quartz
specimens, and because they are still dirty, you need to
know how to clean them. If you have just a few pieces,
use an old toothbrush to get the clay off. Otherwise,
start by building a 2 by 2 foot framed 0.25 inch mesh
screen. You can get this type of screen, called hardware
cloth, at your local hardware or farm and garden store.
Remove the newspaper wrapping and let the specimens dry
on the screen for a couple of days. Keep everything in
the shade to prevent the crystal from heating up too
rapidly in direct sunlight. When the clay is well
cracked and dried, rinse with a garden hose. Let dry a
couple of days and repeat the cycle.
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Removing the iron
Then you are ready for the next step. If the crystal only has
a very light iron staining, then a few days soaking in a weak
oxalic acid solution in a covered plastic bucket will remove
it. If the iron staining is heavy, then we must cook the
quartz in an acid solution. People have many ways to clean
quartz, all involving basically the same scenario. Your
specimens may be coated by iron or manganese oxides, with or
without clay and you wish to remove the staining so the
specimens are as clean as possible.
Use with care
The most commonly used, readily accessible chemical for
cleaning quartz is oxalic acid, which may be bought as a white
crystalline powder. It may be purchased from many mineral
dealers in Arkansas, especially those who specialize in
quartz. When mixed with water at a measure of a few ounces per
gallon and then heated to just below a boil, oxalic acid is
capable of removing all but the most stubborn iron staining.
It is a weak organic acid, but don't kid yourself, it will
hurt you especially if you breath the fumes. So use it only
outside in a protected and well vented area, preferably where
no children may gain access.
Some key points
There are several key points to preparing quartz to be
cleaned. First, you need to remove the clay. This is
accomplished by cycling the specimens through the several wet
and dry periods to loosen and wash the clay away. You may have
to use a pressure washer to remove the last of the clay.
Remember: this first step is critical.
You do not want to have to clean the material several times,
and that is exactly what you will have to do if the clay is
not completely removed before the first acid cleaning. Trim
your specimens to the size and shape you want before cleaning
in acid. Remove the dinged or broken portions. This action
will save the time of re-cleaning after trimming and the cost
of the additional acid used to clean what you trimmed off and
threw away.
Once you have the specimens prepared for acid treatment, then
you must consider the situation. Do you have small specimens
and just a gallon or two of crystals or do you have some big
pieces? Maybe you got lucky and have one piece that would fill
a 5-gallon plastic bucket!
Tips for using oxalic acid
Don't use expensive reagent or chemical grade oxalic from the
pharmacy. Instead, when you visit Arkansas, ask at the crystal
shops around Mount Ida or Jessieville. Many dealers provide
written instructions and sell it by the pound or multi-pound
package for around $3 per pound or $2.50 per pound for 5
pounds. How much do you need to buy? It depends. Did you get a
5 gallon bucket of quartz specimens or a 3/4 ton truck bed
full? A five gallon bucket might take 1 to 1.5 pounds of acid
to 5 gallons of water if the crystal is really dirty.
Start with a weaker solution first and build its strength if
you need to. Also, the acid solution will not be used up until
it turns dark emerald green by becoming saturated with the
removed iron, so you can reuse it by adding a very small
amount of fresh water and powdered acid to the old solution.
Remember: it is an acid, though a relatively weak one. Do not
leave this stuff where kids or animals might get into it. I
usually wear dish washing gloves when working around it even
though it will not burn skin, it will let you know if you have
a scratch or cut, by burning you. Take care not to get any
acid in your eyes. I always keep a garden hose handy so when I
get a splash, I can rinse it off immediately. Accidents
happen!
Experiences with Cookers
To clean small pieces, you need to search for cookers at
yard/garage sales. Whenever you find a crock pot (the slow
cooker ceramic-lined type) for $4 or less, buy it!.You can get
some 10 to 12 processing cycles before the acid finds its way
through a hairline crack in the ceramic inner glaze and
corrodes the heating element. But that's OK, if you got 10
gallons of small quartz specimens cleaned, then it's worth
it.
Place the specimens in the crock pot, add cold water, then a
couple of ounces of dry oxalic acid and top off with cool
water. Be sure the water is above the crystals because any
crystal sticking out will not get cleaned. Cover with the
glass or plastic lid, plug in and set the temperature control
to low. Check this every two days and add a little warm water
as needed to keep the crystals submerged. DO NOT DO THIS IN
THE HOUSE. ACID VAPORS ARE POISONOUS.
After about a week, turn the crock pot off and let it cool
down overnight. Do not get too anxious to pull the crystals
out while they are hot or they will shatter from the thermal
shock. Then remove the specimens and rinse them thoroughly. If
your specimens begins to grow a white powder as they dry,
place them back in a clean crock pot, add water and a 1/3 a
cup of baking soda, and cook overnight. This will neutralize
the remaining acid as it comes out of the nooks and crannies
of the specimens. If this does not work to get rid of the
white powder problem, then you will need to cook them again in
clean water with baking soda as a neutralizer.
Disposing of acid
To dispose of a volume of spent oxalic acid (it will be a dark
emerald green color from the dissolved iron it contains), add
lime (CaO) like you use in the garden to the liquid until you
get no reaction. Then it will be neutralized due to the
formation of harmless calcium oxalate. You can just dump it on
the ground like I do where I wash my crystals with a garden
hose. That way, the next time I wash rocks or it rains the
material is diluted. If you lived in town or in an apartment,
just take a funnel, pour it in a 1-gallon milk jug and put it
in the trash or in a dumpster. Since its neutralized, it is
not considered a hazardous material and since it is
water-based it is not flammable.
This information is an excerpt from Collecting Crystals: A
Guide to Quartz in Arkansas by Darcy and Mike Howard,
©2000
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