Milky white natural quartz crystal cluster from Bulgaria, 501g, on a black background

Bulgarian Quartz

Quartz is silicon dioxide (SiO2), the second most common mineral in the Earth's continental crust after feldspar. It crystallises in six-sided prisms that end in pointed tips and comes in more colours and forms than almost any other mineral: amethyst, citrine, smoky and rose quartz are all quartz, and so are chalcedony, agate and jasper, which are made of crystals too small to see. With a hardness of 7 it scratches glass, and because it produces a small electric charge under pressure, thin quartz plates keep time in watches and electronics.

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Mineral guide

Bulgarian Quartz

Bulgarian quartz

The quartz in this collection comes from Bulgaria. Many Bulgarian specimens come from the lead-zinc deposits of the Rhodope Mountains in the south of the country, where hot, mineral-rich fluids moved through cracks in the rock and slowly cooled, leaving crystals behind. You will find milky white crystal groups, coloured by countless tiny fluid bubbles inside the crystals; sugar quartz, the collectors' name for crusts of very small, glittering crystals; rusty quartz, coated orange by a thin layer of iron oxide; and grey chalcedony with sparkling druzy quartz on top.

Other minerals in these specimens

Quartz rarely grew alone in these veins. Many clusters also carry dark metallic galena, black or green sphalerite, pale calcite or brassy pyrite, which crystallised in the same cracks. The title of each listing names every mineral in the piece, and mixed specimens also appear in the collection of each mineral they contain.

How to recognise quartz

Quartz is harder than steel and glass, so a knife cannot scratch it. It has no cleavage: instead of splitting along flat planes it breaks with curved, shell-like surfaces. Its crystals are six-sided, and the prism faces often show fine horizontal lines.

Caring for quartz

Quartz itself is durable and can be rinsed in water and cleaned with a soft brush. Many clusters also carry softer minerals such as calcite or galena, so dust mixed specimens with a dry brush or a gentle stream of air rather than soaking or scrubbing them.

Each listing shows the weight and photos of the actual specimen.