http://secretsofthesunsects.wordpress.com/2011/12/05/incan-vitrified-stones/ (http://secretsofthesunsects.wordpress.com/2011/12/05/incan-vitrified-stones/)
(figura 2 mi se pare cea mai interesanta, piatra topita a umplut inclusiv denivelarea provocata de crapatura pietrei de dedesubt)
http://www.abovetopsecret.com/forum/thread37367/pg1&mem=IKnowNothing (http://www.abovetopsecret.com/forum/thread37367/pg1&mem=IKnowNothing)