Polished white agate or chalcedony bead

The specimen is a small, smoothly polished, opaque-to-slightly translucent white rounded bead with an irregular brown inclusion or vein. Quartz hardness is approximately 6.5–7 on the Mohs scale; luster is waxy to vitreous when polished; crystal structure is trigonal, although the microscopic quartz fibers in chalcedony are too small to see individually. Specific gravity is about 2.58–2.65. It may show no obvious cleavage and breaks with a conchoidal fracture. The apparent hole is not clearly visible in the image, so it could be a bead or simply a rounded tumbled stone.

Agate and chalcedony form when silica-rich groundwater fills cavities, vesicles, or fractures in volcanic rocks. Layered or banded material develops through repeated deposition of silica, while brown areas commonly result from iron oxides such as hematite or limonite. The exact geological age cannot be determined from the photograph; agates occur in rocks ranging from Precambrian to recent age. The rounded shape and high polish indicate human processing by tumbling, grinding, or carving.

Commonly used for inexpensive jewelry, beads, cabochons, carvings, worry stones, ornaments, and mineral collections. Agate is also used for decorative objects and occasionally precision grinding or laboratory surfaces. This small specimen has primarily ornamental or craft value.

Agate is not a single mineral species but a variety of banded or patterned chalcedony. White chalcedony can resemble porcelain, marble, plastic, or glass, so hardness and specific-gravity testing are useful. Brown coloration in agate is often caused by iron rather than by a separate gemstone mineral.

Likely identification: polished white agate or chalcedony, but the photograph alone cannot rule out white onyx, dyed stone, ceramic, or glass. In the field, natural chalcedony feels cool and dense, will not usually scratch with a steel knife, and can scratch ordinary window glass. A 10× loupe may reveal fine fibrous texture, curved banding, or natural inclusions rather than bubbles typical of glass. Agates are widespread in volcanic terrains and are commonly found in Brazil, Uruguay, Mexico, India, Madagascar, the United States, and many other regions. A drilled hole, if present, would support the bead interpretation; laboratory testing or a close-up of the surface and underside would improve identification.