[Are silicates only gravel stones?]

The presence of silicon dioxide in urinary calculi usually indicates the presence of artefacts. However in isolated cases infra-red and X-ray spectroscopy and electron-ray microanalysis have clearly demonstrated the presence of silicate in crystalline urinary sediment and as a phase of urinary calculi, probably as a result of overdoses of silicon preparations. A local silicon enrichment of up to 2% is certain in phosphate phases and makes an isomorphic incorporation of SiO4 ions probable.