Grindability Inde Correlation. Price For Hardgroves Grindability Inde Machine. 7859hardgrove grindability index limestone price for hardgroves grindability index machine Hardgrove Grindability Index Wikipedia Hardgrove Grindability Index short HGI is a measure for the grindability of coal Grindability is an index therefore it has no unit The smaller the HGI the harder is.