XM2160NQA: Quartz crystals of intense luster cover a hemispherical cavity corresponding to an ancient fossil, probably a bivalve, embedded in a matrix of marly rock formed in a lagoon. These Quartz-filled vugs are very difficult to get today since the locality is now protected and so specimens can only be obtained from old collections, such as that of Santiago Jiménez García in this case.
Quartz geodes outcrop, Valdematilla ravine, Tubilla del Agua, Comarca Valle del Rudrón, Burgos, Castile and León  Spain

Specimen size: 11.8 × 11.1 × 4.5 cm = 4.65” × 4.37” × 1.77”

Main crystal size: 6.3 × 6 cm = 2.48” × 2.36”