Trachyte

Stěnská quarry mined into the slope of Špičák Hill near Teplá Monastery is the only place in the Czech Republic where a pale greyish-yellow to beige rock is exploited for dimension stone and sculpturing purposes. This rock is called trachyte.

Trachyte is a rock closely related to phonolites and similarly to them it forms when the magma evolves (differentiates) for a long time prior to the eruption. Trachytic lavas, as well as the phonolite lavas, are derived from the upper part of the magma chamber, depleted in minerals of magnesium and iron. On the other hand, trachyte is rich in minerals containing silica, aluminium, sodium and potassium, namely alkali feldspars. Typical attribute of trachytes is the fluidal arrangement of feldspar crystals in their texture (called trachytic texture).

Trachytic lavas are viscous (like honey) and extensive lava fields are therefore rare – for example Třebouňský vrch Hill. Trachytes typically form lava-domes like Špičák or Prachometský vrch Hill. In Doupovské hory Mts, trachytes are present as dikes, like the small dike-swarm on the sierra-trail between Ovčí vrch and Složiště Hills.

Sample donated by the company Lom Hamr, Ltd.