Specimens of pure white marble from distant localities may be practically indistinguishable by macroscopic methods. Among other methods, detn. of trace elements can serve to differentiate between marbles from different ancient quarries, which is of vital interest for classical archaeology. In the course of a trace-element determination by means of x-ray spectroscopy, Na and Mn contents of about 230 specimens from quarries in the Aegean Islands and Attica (Greece) and Western Anatolia (Turkey) were analyzed by neutron activation. Flat rock fragments weighing about 300 mg. were broken out of hand specimens, carefully avoiding weathered parts near the surface or along joints. They were then activated for 30 hours with 3. 6 X 10¹² slow n/cm. ^2-sec. gamma-Spectra of ²⁴Na and ⁵⁶Mn were measured with an RCL 512-channel analyzer. The Mn contents vary between 0.5 and 200 ppm., the Na contents between 2 and 300 ppm. Na and Mn contents in specimens from the same quarries have a similar range. The Mn concentrations, especially when combined with other data, enable some types of marble which were preferentially used by the ancient Greeks to be distinguished. -- AATA