Originally published at: A guide to growing large and flawless salt crystals | Boing Boing
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Here are a few we made earlier…
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One step closer to my dream of single-crystal rock candy …
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Worth noting that if you grow salt crystals that they need to be kept in very dry conditions. sodium chloride is hygroscopic and absorbs water vapour from the atmosphere so the crystals will ‘bloom’ unless they are protected. A sealed container with a few silica gel packs will keep them safe.
This takes me back to my many unsuccessful childhood attempts to grow large crystals of potassium alum and copper sulfate using the same method. The local chemist did very well out of all my purchases, but probably thought I had some weird medical condition.
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The photos from that cave are incredible.
A bit easier to find is a type of igneous rock called a pegmatite which has a similar composition to granite but has much larger crystals. They form from the last part of granitic magma when magma contains few crystallisation nuclei and is saturated in water and fluxing agents such as chlorine, fluorine and boron that become more and more concentrated in the residual melt.
So the crystals, often of unusual minerals like beryl and tourmaline, grow incredibly slowly and can become enormous - the largest single crystal in the world is a beryl something like 18m long and weighing more than 350 tonnes found in Madagascar. There are also some massive pegmatites in the Appalachians with individual feldspars weighing more than 200 tonnes!
I used to have some lovely pieces of pegmatite containing beautiful black tourmaline (schorl), massive sheets of silver lithium micas like phlogopite and perfect pale green apatite I collected from a landslide at Megilligar Rocks in West Cornwall - I wonder where that ended up in all my moves over the years?
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Dang. I have been going to Cornwall for my holidays all my life and never found any crystals. North Cornwall may not have as many as the south, but maybe I am not trying hard enough. I could pick up any number of crystals at Arthurian woo-mongers, but That Is Not The Same Thing.
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Head West young man to the granite!
There are some spectacular mineral lodes in the region, if they liked tin or copper there are usually some cool metal minerals - though the site of the old mine which produced a unique, gorgeous fluorescent uranium phosphate mineral called torbenite is now under a football pitch. Which may be a good thing…
The North of Cornwall is generally mineralogical dull as it is nothing more than a pile of folded mud - though the folding is spectacular - and there are almost no good fossils.
Although I should point out that Megilligar is now protected as a site of special scientific interest and it is illegal to collect samples.
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