A large-format Japan-law Quartz twin from the well-known crystal district of Diamantina, Minas Gerais, Brazil, a region where twinned quartz is an unusual and infrequent outcome of pocket formation. The two primary crystals meet at the characteristic 84°33′ axis angle that defines this specific twin law, with parallel prism faces emphasizing that the crystals grew together while still remaining visually distinct as individual forms.

The specimen shows a solid crystal presence with a bright, natural luster and well-developed prism faces that reflect light with a clean luster. The crystals have a slightly compressed profile, displaying faint horizontal growth line patterns that cross the prisms at right angles to the main axis. One of the terminations carries a gentle partial penetration zone, giving the twin a layered, interlocked look, while the opposing crystal extends outward in a balanced, off-center symmetry. Matrix contact is limited to the base where the twin originally detached from the pocket, leaving the overall twin form fully intact.

At 20 × 16 × 4 cm, this is a particularly large example for the Japan-law twin habit, a size seldom encountered for this structural type from the locality. The piece carries a natural aesthetic and strong crystal form, clear twinning geometry, and minimal damages from pocket contact making it a solid and highly recognizable twin reference for collectors, who value structural habits over perfection.