'psammitic' originates from Greek, specifically the word 'psámmos', where 'psamm-' meant 'sand' and the adjectival suffix '-ic' came from Greek/Latin meaning 'pertaining to'.

'psammitic' changed from the geological noun 'psammite' (used in 19th-century English and French) which itself was borrowed from Greek 'psámmos'; 'psammite' then produced the adjective 'psammitic' in modern English.

Initially, it meant 'of or relating to sand', but over time it evolved into the more specialized geological sense 'relating to psammite or sandy/metamorphosed sandstone'.