Coyamo / Santa Ulalia Thundereggs

One of the kings of Mexican thunderegg and not particularly rare. The matrix is distinctly smooth and uniform, but ranging from a light tan to a rich chestnut, sometimes with fairly distinctive invasive staining. Sometimes they edge towards a granular texture. The majority of the cores seems to be hollow with thin agate bands, sometimes leaning towards cloud agate - but that is not to say that solid cores are rare, as can be seen below. The agate is usually white, grey and clear, but can also verge into the pink. Black intrusions and decay are also common.