References in the ancient sources indicate that the Libyan desert was a source of ‘carbunculi’: semiprecious red stones and gemstones variously interpreted as ruby, garnet and spinel, amongst others. While gemstones are not attested in the geological strata of Fazzan (south-west Libya), a range of silicabased stones including chert, chalcedony, agate and carnelian are known to originate in this area, linked to an early civilisation known as the Garamantes. It has been long proposed that the geochemical signature and the variations in the relative proportions of quartz:moganite phases can be used to distinguish between groups of stones of different origin. The proposed methodology was tested on a number of archaeological samples from the Garamantian sites of Jarma (ancient Garama) and Saniat Jibril, in Fazzan. Fragments of chert, carnelian and amazonite found at the two sites have been identified as raw materials associated with beadmaking. Trace elemental data obtained by LA-ICP-MS were combined with mineralogical data obtained by X-ray powder diffraction and Raman spectroscopy on the same samples and a group of reference samples. The dataset has been compared with the available literature and data from other localities around the world. To this purpose a preliminary database of silica-based materials was established for provenance work. Based on the scarce data available in the literature, the importation of these stones from Eastern localities such as India may be ruled out. The measured data on archaeological samples and debitage allow us to define a reliable reference group of parameters for materials from Fazzan, which are likely to be derived from a unique geological source. The methodology should be extended and compared with cherts and carnelians from a range of Mediterranean and Sub-Saharan sites. This characterisation work is a tool of high potential utility for a new investigation of ancient contact and trade across the Trans-Saharan zone.