Mesozoic Era · Cretaceous Period Approximately 145 to 66 million years ago This is an exquisitely preserved dinosaur egg fossil specimen; distinct eggshell textures and the original form remain visible on the exterior. Over tens of millions of years of geological evolution, the organic matter inside the egg decomposed to form a hollow cavity. Mineral-rich groundwater seeped into this space, and through prolonged precipitation and crystallization, a mass of milky-white crystals formed, coating the interior and transforming the specimen into a rare "natural dinosaur egg geode." The exterior of the shell is reddish-brown and tightly bonded to the sedimentary rock matrix, revealing clear shell layering and growth lines. The interior crystals range from milky-white to translucent, featuring fine crystal faces and a vitreous luster; they are likely carbonate minerals (commonly calcite).