The brown markings are remnants of the host rock in which the mineral formed. These spidery veins are correctly known as matrix. They can often help with correct identification.
The Sleeping Beauty mine in Arizona was once the world's largest producer of a sky blue coloured turquoise with little or no matrix. Mining operations ceased in 2012 and the deposit is now a copper mine.
Turquoise has been mined for thousands of years and is well known around the world. Its colour can vary widely depending on where it was mined.
Turquoise is one of the very few minerals to have given its name to a colour.
A beautiful large turquoise cabochon that could be used to create a unique piece of jewellery. It could also be used for its metaphysical properties.