The hollow lined with crystal points. Where dyed and 'enhanced' material shows up most.
Brazil, Uruguay, Zambia, Madagascar, Arizona3 references
A geode is a cavity in volcanic rock lined with crystals grown inwards from the walls. The large amethyst 'cathedrals' in shops are sections cut from such cavities in Brazilian and Uruguayan basalt, and they are the commonest place to meet enhanced amethyst, because the piece is big, expensive and sold on colour.
Two treatments turn up. The first is dye, sprayed or soaked into pale material — look at the base of the crystals where they meet the rock, and into the crevices between points, because that is where dye pools. Natural colour is strongest in the outer tip of each crystal and fades towards its base, which is the opposite pattern. The second is heat, which turns amethyst to citrine; almost every large orange 'citrine cathedral' on the market is heated amethyst, and the honest ones say so.
Provenance genuinely matters for price here. Uruguayan material is typically deeper in colour with smaller, tighter crystals; Brazilian is usually paler with larger points. A vendor claiming Uruguayan depth at Brazilian prices is worth a second look at the crevices.
Uruguayan (deep, small crystals) · Brazilian (paler, larger crystals) · Cathedral / church
Establish which of these you are holding before judging it. A genuine piece read against another reference's rules will look wrong when it is not.
These apply to this model and not to the rest of Amethyst. Work them alongside the maker's general checks, not instead of them.
In natural material each crystal is deepest at its tip and pales towards its base, because the iron concentrated in the last-grown layers. Dyed geodes show the reverse: colour pooled down in the gaps between points and at the roots, where the liquid ran and settled.
On a surface-dyed piece, some dyes lift onto the swab. Do it somewhere that will not be seen, and take a clean result as inconclusive rather than as proof — many dyes are fast once dry.
Natural citrine of that size and saturation is rare to the point of near-absence. Look at the base of the piece and in shadowed pockets for surviving purple, which is the direct evidence of what it was before the kiln.
Priced by size, colour depth and crystal quality. Small geodes are tens of dollars; large deep-purple Uruguayan cathedrals reach four figures.
An orientation for honest, unrestored condition — never an appraisal, and never a quotation.
Lovenhall StoneThe tests tell you what it is. The instrument reads a photograph and offers a name to start from — then hands you back to the tile and the coin, which are what settle it.