Whiskey rocks are 1" cubes of rock designed to be placed in the freezer, and added to a drink to chill it without diluting. They are typically sold at exorberant prices for what is essentially polished rock.
Given the idea of making one's own,
What rocks would work for heat capacity (cooling ability) and not imparting flavor?
Searching a bit resulted in the following answer: Whiskey rocks are made of solid (or milled) soapstone (source).
Though, there seem to be more kinds of whiskey rocks. This site shows different ways to cool your whiskey with a chart, which shows which way cools for the longest time. Cubes, rings or balls of steel seem to work the best. Cleaned properly, I don't think they will affect the flavor of your beverage.
If you have the tools to work on steel I would recommend this rather than making your own whiskey rock.
