As a compost practitioner and scientific layman, I am always interested to know a more scientific topic on composting. I have always recommended shredding to speed up the breakdown of woody materials. I have used lime in the past but to counteract acidity if there has been a lot of fruit waste in the mix.

What I am intrested in finding out is if there is a more environmentally friendly alternative to the use of lime which requires some form of mineral extraction from the earth? Or is there a source of lime for which the extraction has a minimal impact?