Just a quick post - after reading Wulf's article here on calc, and being reminded of my own post here, again on the subject of calc, I thought I'd have a look at the etymology of the word.
In the Anglo-Saxon runes, we do indeed have the calc rune. The old English word was 'cealc' however the root is not Germanic - it is borrowed from the Latin. Common Germanic words for chalk centre around the root 'lim' which gives us lime, limestone etc.
To find the root of the word chalk, we have to go back to the Proto Indo-European. The word is still used today in India - the city of Calcutta for example takes the name from the root Calc - but it is not named after Kalki, but the Dark Goddess Kali. What is interesting is that Kali is also called Kāla - which is rooted in Kal (calc) but means 'Black'. The balance of light and dark!