A Little Clean-Up

Mineral collectors are often frustrated to find that a beautifully shaped crystal is coated with rust from

the iron in the surrounding soil or water. With same strong acid, baking soda and safety precautions, you can get the rust off and find the hidden colors.

This week I went to a small spot that is loaded with a rare gemstone called sillimanite. There were beautiful conical crystals exposed on the outside of the rocks, just lying on top of the soil. The crystals are a silky gray mixed in with brown smoky quartz, whit feldspar, and some bright red minerals, too. But, the area is rich in iron. Everything was orange.

Then comes the cleaning.

There are various chemicals used to clean rust off of relatively inert minerals, like quartz. Many people use drain cleaners like CLR or Iron-off, which are available in bathroom cleaning aisles everywhere.  I find that these are too weak and are used up before the rust is gone. They are very slow, too. One site suggested leaving the rocks in the acid for no more than 20 minutes. It took me a couple days to get the rust off with several fresh baths. 

I used something considerably stronger: muriatic acid (hydrochloric acid) from the pool supply store. It's incredibly caustic. I only use it outside because even my lab's vent fan has its limits. And I wear lots of safety gear! Breathing these fumes will do very bad things for your lungs in very short order. Getting it on your skin will cause a serious chemical burn. This is not something to do anywhere near children. I cannot emphasize the safety gear enough. 

I brought home my treasures and donned my gear: Long sleeves, acid-resistant gloves, goggles and respirator. 

I placed the samples in a plastic bucket and gently poured the acid to cover them. Then I covered the bucket and let them sit overnight.

The next morning, in full safety gear, I returned to my deck. One at a time, I took the rocks out of the acid with a pair of tongs and placed them in a fresh, dry bucket. I sprinkled them all over with baking soda until the fizzing stopped, then used the tongs to transfer them to a bucket of clean water to soak overnight again.

Much better! The golden brown was nice, but having everything I collect rusted golden brown is a little monotonous. Here you can see just how much of this rock is sillimanite.