There are several sculpted quartz crystal skulls - portraying human skulls in both natural and miniature scales - that are reportedly of ancient Mesoamerican origin. Of the examples made available to scientific scrutiny, none have been proven to be of ancient manufacture nor Mesoamerican origin - instead, most are of 19th-20th century European origin, displaying traces of modern tools/machinery and modern grinding/polishing compounds. None of the known crystal skulls in museum (or private) collections have documented proof of their origins - such as being found in an archaeological excavation, etc. Though some skulls may have stories or legends of archaeological provenience - such as the famous Mitchell-Hedges Skull [photo above] - no known archaeological field reports verify these claims.
At a stylistic level [note: I am a specialist in Mesoamerican iconography, having a PhD dissertation and academic publications on the subject], the lapidary/art style of the crystal skulls does not reflect the style of known Mesoamerican stone artifacts. In simple terms - they do not look like Mesoamerican stone objects, they are stylistically "off." Also, though some artifacts of quartz crystal have been recovered from Mesoamerican archaeological sites, quartz (and crystals) do not appear to have been of great importance among ancient Mesoamerican societies (beyond novelty and some aesthetic appeal) - there are no (legitimate) sources that indicate that crystals figured into ancient Mesoamerican religious or spiritual beliefs. However, several modern Mesoamerican religious practices do incorporate crystals (such as some Yucatec Quiché Maya divination practices).
