钙质 vs.
钙:
钙 (gài) is the chemical element calcium (used in chemistry);
钙质 adds
质 ('substance') and is the everyday/nutritional word — what you 'eat' or 'lack'. The pattern X+
质 ('X-substance') is productive for nutrients:
蛋白质 (protein),
脂质 (lipid),
矿物质 (mineral).
