I've had terrible results with granite as a base for HI-Fi equipment but if you must have it, the best thing to buy is a machinist base, designed for a tool maker / machine shop.
These cost a fraction of what similar materials sell for in the funeral business and audio business.
Here is an example of a precision machine base that's 9"X12" and weighs nearly 60 pounds, yet sells for only $22.00 because it's intended for tool rooms.
http://www.wttool.com/p/1312-0006?utm_id=44
I went through this nearly 10 years ago, hope you have better results with stone than I did.
These cost a fraction of what similar materials sell for in the funeral business and audio business.
Here is an example of a precision machine base that's 9"X12" and weighs nearly 60 pounds, yet sells for only $22.00 because it's intended for tool rooms.
http://www.wttool.com/p/1312-0006?utm_id=44
I went through this nearly 10 years ago, hope you have better results with stone than I did.