Topacio
Topacio is a mineral with formula Al₂SiO₄(F,OH)₂, in the Silicatos (Nesosilicatos) group. This specimen comes from San Felipe, Comonfort, Guanajuato, México and joined the Terrium collection in 2025.
Description
Group of crystals with well-defined pyramidal terminations, pale rosé-pink colour and vitreous lustre. The largest crystal, 2 cm, projects from the edge of a vesicular cavity, surrounded by smaller individuals lining the interior of the vesicle. The light grey, porous matrix is solidified rhyolitic lava with an ashy appearance. The piece retains the original volcanic context, which adds value.
History of this specimen
I note it was collected personally by the Mexican collector Daniel Pérez after six months of fieldwork (March to September 2025). The search was extremely difficult: many cavities were empty and, where there were crystals, they had often detached along cleavage due to stresses and movement.
About Topacio
Topaz is a nesosilicate with Mohs hardness 8, valued for its transparency, vitreous lustre and perfect cleavage in one direction, which makes it resistant to scratching but fragile on fracture. Specimens formed in volcanic cavities, like this one, are much less common than pegmatitic ones and usually show more irregular forms and interrupted growth, testimony to the eruptive environment.
About the locality
The locality of San Felipe, in the Mexican state of Guanajuato, is noted for its rhyolites rich in vesicular cavities, where topaz occasionally crystallises. These cavities formed from gas bubbles trapped during the solidification of the lavas, and their exploration requires meticulous work, as only a small fraction contain well-developed crystals.
Technical data
- Catalogue No.
- 0204
- Composition
- Al₂SiO₄(F,OH)₂
- Name
- Topacio
- Group
- Silicatos (Nesosilicatos)
- Category
- Cavella
- Matrix
- Riolita vesicular
- Mine
- San Felipe
- District / Municipality
- Comonfort
- Province
- Guanajuato
- Country
- México
- Size (cm)
- 3.5 x 3.5 x 3.5
- Acquired
- 2025
- Ex-collection
- Daniel Pérez
- Etymology
- From the Greek "topazos", name of an island in the Red Sea (now Zabargad), although the mineral described then was not topaz.
- Quality
- Muy buena
- Value trend
- Estable