What is the name of the mineral used to make the pigment 'cobalt blue'? - Quora

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What color is the most difficult to make, someone says it's Blue? - Quora

What are the things that look like blue in colour? - Quora

Is Tanzanite a rare gemstone? - Quora

What color is the bluest? - Quora

In geology, what is Blue John? - Quora

What is the best color of blue? - Quora

What is turquoise, and where does it come from? - Quora

What is Turquoise? - Quora