Quartz, Las Vigas, Vera Cruz, Mexico.
This semi-precious violet gem is commonly known as amethyst.
Source: Museum Victoria
Beryl, Wah Wah Mountains, Utah, United States of America.
Source: Museum Victoria
Diamond, Beechworth, Victoria, Australia.
Image: Frank Coffa
Source: Museum Victoria
Some volcanic rocks contain crystals of minerals that are gemstones. Topaz and beryl are found in silica-rich volcanic rocks, while ruby, sapphire and peridot occur in basaltic rocks. Diamond, the most valuable gemstone, crystallises in the Earth’s mantle and is brought to the surface by explosive volcanic eruptions.