Biotite Lenses ("Birthing Stones")

"Pedra parideira" - birthing stone - so call the Portuguese the remarkable biotite lenses found in a rocky mountain range in northern Portugal. They are a metamorphic mica concretion with a feldspar core. They have only been found in this one few acre areas in Portugal. The bed rock, ca... 300 million year-old granite was metamorphosed by the pressure and heat of movements in the earth´s crust. Thus, the biotite lenses occur in an exactly northeast-southwest direction. Just as strange as the virtual existence of the birthing stones, is the phenomenon that one can observe at the site on hot days in July after the summer solstice and on frost sparkling January days after the winter solstice. The biotite lenses really are birthed. Everywhere in the rock it crackles and pops. Once in a while one hears an actually loud crack. And the black lenses come in large masses to light. Thereby, they cleave away at times whole plates of ton-heavy granite. But this birthing process occurs only during very hot or cold spells. Normally, the "pedras parideiras" slumber peacefully in Mother Earth. The native people, progeny of the Celts, as their blue eyes and blond hair attest, guard the biotite lenses as a treasure. No house in the region is without at least one lens in the window sill. They bring the people fertility, luck, energy, and protect against evil spirits - no wonder, when the "parideiras" even overwhelm the granite. Due to the uniqueness of the biotite lenses, in 2007 a geological park was established in the area. All birthing stones that are offered were found before the year 1990.

Price List Biotite Lenses






Size in cm

 (Diameter ca.)


Price in €





Biotite Lense - Size 1

4.0 – 4.5







Biotite Lense - Size 2

4.5 – 5.5







Biotite Lense - Size 3

6.0 – 8.0







Biotite Lense, drilled - Size 1

2.5 – 3.5

Pendant, 2,5 mm drilling






Biotite Lense, drilled - Size 2

3.5 – 4.5

Pendant, 2,5 mm drilling


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