Benitoite Mine - Raw material

Updated September 20, 2008

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Specimen Preparation - How to Clean Them

By, John Veevaert
Trinity Mineral Co
Weaverville, California

So, what does it take to get a cleaned specimen of benitoite and/or neptunite? Attractive specimens of this beautiful mineral assemblage just don't happen - they are literally crafted! The process involves several steps which are all time consuming and require a bit of artistic aptitude. One thing to keep in mind the whole time is that removing matrix is a one way procedure. Once it is removed it can not be put back. Too much removal is as, if not more, detrimental to the finished specimen as leaving too much is.

Initially, uncleaned specimens are rinsed in water to remove as much of the clay and mud as is possible before immersion in the acid bath. Mud and clay from this mine is some of the most tenacious crud in the world. It is really stuck on there! After the initial rinsing I place the specimens in an acid bath to do a preliminary etching - generally removing 1-2 mm of the natrolite. Next the specimen is assessed for waxing needs (paraffin or wax are the same thing). Wax is used to impede etching where natrolite is desired with the finished specimen. I use a hot plate with melted wax in an old pot then use a brush to dab it on in places I want protected. I also frequently dip the sides of the specimen in the melted wax where it is easy to do so which speeds that step up a lot. Once the desired waxing is completed I place the specimen in an acid bath with the strength of the hydrochloric (HCl) acid (muriatic acid is the same thing as HCl) at 5-7 parts water to 1 part acid. The natrolite is slowly dissolved to a soluble gel (The natrolite dissolves like salt does in water. There is no effervescence!) which can be removed by running water and/or very light brushing. As crystals begin to emerge from the natrolite it is necessary to wax portions of the specimen to prevent an undesired loss of natrolite (The natrolite provides a pleasing contrast to both the benitoite and neptunite crystals. Too much etching leaves some crystals precariously perched by a thread or totally ruins the aesthetics of the specimen). Once the desired amount of wax is applied the specimen is returned to the acid bath and etching continues. Once the desired level of etching is reached the wax must be removed which is done chemically or by a heated water bath. First I rinse the specimen and soak it in water. Next, the acid needs to be neutralized and wax removed. I place the specimen in a pot filled with a solution of water and sodium hydroxide and then place it on a hot plate. The solution with the specimen is then brought to about 80-85 C^o or about 180 F^o. The heated solution melts the wax and the base acts as a wetting agent to lift all of the wax off the specimen and also to completely neutralize the acid that entered the specimen during the long periods of soaking. Once the wax has melted off the specimen I let the pot cool slowly to room temperature. The melted wax floats to the surface of the pot and when cool is easy to scoop out and reuse if you want to. The specimen is then placed in water and allowed to soak. It is rinsed several times more in water to remove the base then allowed to dry. Final cleaning can be done with additional chemicals that are very dangerous to use so I advocate the use of a toothpick or dental tool and a quick bath in an ultrasonic. To be done right an average specimen requires no less than 8 hours of personal attention. Many require a great deal more! In the past I have personally spent over 36 cumulative hours just on one rock! It is easy to see why specimen prices are what they are for this rare mineral given the amount of time it takes to make these specimens look the way they do! Even then the labor costs of cleaning these for many specimens is never fully recovered...

The following are a set of pictures to show what specimens looked like before they were cleaned and after. They also show several of the steps needed to take what looks initially like a piece of rubble and transform it into a finished specimen of high quality.
I have selected a specimen that initally weighed 590 grams (0.59 kilograms). It's initial dimensions were 12x 11.8 x 5 cm. Final dimensions are 12 x 9 x 4.2 cm and it weighs 430 grams (0.43 kilograms).

This shot shows the specimen after its first 1 hour soak in acid. Note the large chunk of crossite before it was removed. There are several crystals of neptunite visible that are all damaged except for one. Also visible are crystals of benitoite and joaquinite. In my mind this has the potential to be a very good joaquinite specimen. Here's the rock photographed from the other side. At this point I have already waxed it along the edge and I have covered the undamaged crystal of neptunite.

These two shots show the wax that has been applied to the edge of the specimen. Note that I have not entirely covered the benitoite crystal visible. I wanted to make sure that it was not completely bared of all natrolite until I was sure that the joaquinite was a plentiful as I thought it would be. This shot shows waxing along the edge and also a number of joaquinite crystals and a busted neptunite.

Here's the before right after the good neptunite has been waxed. Note - I covered the entire area here and later had to remove the wax and then re-wax the specimen. This shot shows the same area after etching and cleaning are completed. There is absolutely no sign of the additional neptunite crystals next to the one that was protected. Also note that the damaged crystal next to the good one is gone.

Here's the rock after several days of drying after the last rinsing. Note that there is a yellowish staining. This is evidence of acid that leached to the surface. Still not done with this thing!! Fortunately, water soaking and rinsing are all that are needed to cure the problem. All that is needed is time. In this case about 24 hours.

Here's a closer view of the yellow staining. And after the final rinsing.

Here's a close view of a residual damaged neptunite crystal. And here is the same view after the damaged crystal has been removed using a dremmel tool. There is a little sacrafice of some small joaquinite crystals but it is acceptable given that there are literally hundreds of joaquinite crystals on this specimen.

Here's a close up of a 1.0 cm crystal of benitoite in a field of 1/2 cm crystals of neptunite and dozens of 1 mm crystals of joaquinite. Here are two damaged crystals of neptunite that no longer exist in the final specimen.

Here's the final deal. Hundreds of joaquinite crystals as I suspected and two 1+ cm crystals of benitoite and dozens of additional undamaged neptunite crystals to 1.9 cm in length that were completely hidden!! I have left scattered areas of natrolite which provide a nice contrast but removed enough to show the large number of joaquinite crystals. There are more under the natrolite but enough are exposed to get the point across. Also note the missing chunk of matrix visible in the photo on the right. That was removed using a Zuber Trimmer. And here it was at the very beginning.

Total time from start to finish about 8 days.
Actual time I spent on this specimen about 12 hours.
This specimen is for sale at $500.00 - IT IS NOW SOLD
This specimen would have cost someone about $39.00 if it had been placed in an order of mine run.
Many specimens of this type have been sent off to folks already.

Here's two shots of the same rock before cleaning. In this photo it has only been give a 1 hour acid bath. In this photo it has been waxed along the edges.

Here's the final deal. 5.8 x 2.7 x 2 cm specimen of natrolite and crossite with two brilliantly lustrous and undamaged crystals of neptunite to 2.1 cm in length. Both crystals are fully and sharply terminated. Note that some of the matrix was removed. I will likely remove more in time and may even eliminate the smaller crystal all together. A close up of the two crystals.

Initial weight of the specimen was 34.6 grams. Final weight is 21.5 grams. Total time from start to finish about 4 days.
Actual time I spent on this specimen about 3 hours. This specimen was for sale at $95.00 IT IS NOW SOLD. This specimen would have cost someone about $2.30 if it had been placed in an order of mine run. Many specimens of this type have been sent off to folks already.

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This shot shows the specimen after its first 1 hour soak in acid. Note the large chunk of crossite before it was removed. There are several crystals of neptunite visible that are all damaged except for one. Also visible are crystals of benitoite and joaquinite. In my mind this has the potential to be a very good joaquinite specimen.	Here's the rock photographed from the other side. At this point I have already waxed it along the edge and I have covered the undamaged crystal of neptunite.


These two shots show the wax that has been applied to the edge of the specimen. Note that I have not entirely covered the benitoite crystal visible. I wanted to make sure that it was not completely bared of all natrolite until I was sure that the joaquinite was a plentiful as I thought it would be.	This shot shows waxing along the edge and also a number of joaquinite crystals and a busted neptunite.


Here's the before right after the good neptunite has been waxed. Note - I covered the entire area here and later had to remove the wax and then re-wax the specimen.	This shot shows the same area after etching and cleaning are completed. There is absolutely no sign of the additional neptunite crystals next to the one that was protected. Also note that the damaged crystal next to the good one is gone.


Here's the rock after several days of drying after the last rinsing. Note that there is a yellowish staining. This is evidence of acid that leached to the surface. Still not done with this thing!!	Fortunately, water soaking and rinsing are all that are needed to cure the problem. All that is needed is time. In this case about 24 hours.


Here's a closer view of the yellow staining.	And after the final rinsing.


Here's a close view of a residual damaged neptunite crystal.	And here is the same view after the damaged crystal has been removed using a dremmel tool. There is a little sacrafice of some small joaquinite crystals but it is acceptable given that there are literally hundreds of joaquinite crystals on this specimen.


Here's a close up of a 1.0 cm crystal of benitoite in a field of 1/2 cm crystals of neptunite and dozens of 1 mm crystals of joaquinite.	Here are two damaged crystals of neptunite that no longer exist in the final specimen.


Here's two shots of the same rock before cleaning. In this photo it has only been give a 1 hour acid bath.	In this photo it has been waxed along the edges.


Here's the final deal. 5.8 x 2.7 x 2 cm specimen of natrolite and crossite with two brilliantly lustrous and undamaged crystals of neptunite to 2.1 cm in length. Both crystals are fully and sharply terminated. Note that some of the matrix was removed. I will likely remove more in time and may even eliminate the smaller crystal all together.	A close up of the two crystals.