Lemon Quartz: Reduce anxiety & increase concentration. The Gemstone with a flashing and bright yellow color, Lemon Quartz, is a brilliant & unique gemstone that is also known as a silicon dioxide crystal. This crystal is also famous as an alternative birthstone for the people who are born in February, which helps them to eliminate distractions, decrease negativity, reduce anxiety & increase concentration. They are mainly mined in the sedimentary, igneous & metamorphic rocks of Brazil.