Trancas is one of many sites for Mexican "geodes", which are opened on agate-shows before the eyes of the buyer. The moment of surprise and the underlying idea to behold something that no man saw before - this offer is very attractive for visitors. This type of geodes belongs as well as the "coconut geodes" from Las Choyas to the "Thundereggs". The quartz formations in Trancas geodes are wrongly referred as "Scepter-Quartzes". They are arbitrarily piled up however, because their main axes have arranged not parallel. The quartz aggregates often are consisting of winding units, which are severely twisted. Geodes from Trancas fluoresce in ultraviolet light often strongly yellow-green.
Agates from Trancas are traded very rarely, because already at the finding site the closed geodes are divided into different classes, depending on the proportion of the cavity,. The so-called "solids" (massive balls), which could include agate, are not offered on the market. Agates from Trancas are mostly very dark in colour. In addition to classic fortification-agate also “water-level-agate” does occur.
Jeffrey Anderson is describing this location on his website dwarve´s earth treasures.