Yellow calcite (likely polished/tumbled)

Translucent lemon-yellow material with a glassy to waxy luster and prominent internal cleavage-like fractures; calcite has Mohs hardness 3, rhombohedral crystal structure, perfect rhombohedral cleavage, and specific gravity about 2.71. The rounded form appears polished or shaped, and color may be enhanced or confused with dyed chalcedony or resin.

Calcite forms in sedimentary limestones, hydrothermal veins, cavities, and caves, from Precambrian to modern geological ages. Yellow coloration commonly results from iron or other trace impurities.

Used for cement, lime, construction aggregate, optical devices, and mineral collecting; attractive transparent pieces are decorative but generally inexpensive.

Calcite effervesces strongly with dilute hydrochloric acid or household vinegar when freshly scratched. It is much softer than quartz and can be scratched by a copper coin.

Common worldwide, including Mexico, the United States, Iceland, and China; test a hidden area for acid reaction and hardness, while avoiding damage to polished specimens.