A sky blue shade in turquoise is due to the presence of copper, while iron gives it a greener tone.Ochre and brown-black veins in the stone occur during the formation of turquoise, caused by inclusions from nearby rock fragments or from oxide staining.
So when a mineral grain forms (specifically, when it first cools below its trapping temperature), it effectively sets the uranium-lead "clock" to zero.Turquoise is a relatively soft gemstone, and can be easily scratched and broken.This porous opaque stone is easily discolored by oil and pigments, and changes color when it loses some of its water content.Uranium comes in two common isotopes with atomic weights of 235 and 238 (we'll call them 235U and 238U).Both are unstable and radioactive, shedding nuclear particles in a cascade that doesn't stop until they become lead (Pb).The gemstone usually develops in rock near water tables, located in semiarid and arid environments.
The chemicals in turquoise come from adjacent rock, leached out by rain and groundwater.
Uranium minerals themselves are too uncommon to be very useful in dating.
The most common dating method involves the use of minerals like zircon and monazite that are relatively common in granitic rocks.
Lead atoms created by uranium decay are trapped in the crystal and build up in concentration with time.
If nothing disturbs the grain to release any of this radiogenic lead, dating it is straightforward in concept.
Thus any of the radioactive isotopes and its lead daughter product can be used for dating, or a combination may be used.