Stones, explained
How they form, where they come from and what they've meant to people, from the family that buys them at the source.
What is jasper? The patterned stone family explained
What jasper actually is, how its patterns and pictures form, and why mookaite, dalmatian and bumblebee 'jasper' aren't quite the same stone.
What is kyanite, and why does it have two hardnesses?
Kyanite's old name means 'two strengths': it's genuinely softer along the blade than across it. What that tells you about the crystal, and where it comes from.
What is tiger's eye, and why does it shimmer?
How tiger's eye forms from fibrous crystals, why it shows a moving band of light, the difference between gold, red and blue, and how to spot the real thing.
Why optical calcite makes everything look doubled
Look through clear calcite and letters underneath split in two. The physics of double refraction, a 1669 discovery, and a vinegar test for real calcite.
Garnet vs ruby: how to tell two red stones apart
Garnet and ruby are both deep red and both used in jewellery for centuries, but one is corundum and the other a whole family of minerals. How to tell them apart.
What is chrysocolla? The blue-green copper mineral explained
Chrysocolla is a soft, blue-green copper silicate often mistaken for turquoise. How it forms, why it's usually found with malachite, and how to tell them apart.
Why pyrite is called fool's gold
Pyrite forms in the same veins as real gold and shares its colour, which is exactly why it fooled so many prospectors. How to tell the two apart.
Aventurine vs jade: how to tell them apart
Aventurine and jade are both carved into green beads and ornaments, but one is a sparkling quartz and the other one of the toughest rocks worked by hand.
What is lepidolite? The lilac mica explained
Lepidolite is a lithium-rich mica, not a quartz or feldspar. Why it's purple, where it forms, why it glitters, and its odd history as a lithium ore.
What is Himalayan quartz, and how is it different?
Himalayan quartz is clear quartz dug by hand at high altitude. What the name actually promises, why the crystals are so clean, and the green chlorite inside some pieces.
Lapis lazuli vs sodalite: how to tell them apart
Lapis and sodalite are close mineral cousins and easy to confuse. The gold-flecks test, the colour difference, and why one cost more than gold and the other didn't.
How geodes form, from empty bubble to crystal lining
Why some geodes are hollow and crystal-lined while others are solid agate, why so many are amethyst, and how to spot a dyed or glued fake.
How to tell real fluorite
Fluorite gave the word 'fluorescence' to science. What makes it glow under UV, why it cleaves into octahedrons, and how to spot dyed glass sold as it.
Why is pietersite called storm stone?
Pietersite is tiger's eye shattered and re-cemented by silica, so its chatoyant fibres swirl in every direction. Where the storm pattern and its colours come from.
Why India's road quarries are full of crystals
How apophyllite, stilbite, scolecite and cavansite grow inside the Deccan Traps basalt of western India, and why the best specimens come out of ordinary stone quarries.
Ruby in kyanite, fuchsite or zoisite: how to tell them apart
Three rocks with ruby in them: what each one is, where it comes from, and how to tell ruby in kyanite, ruby in fuchsite and ruby in zoisite apart at a glance.
Why amethyst is purple, and what turns it yellow
Iron, natural radiation and heat: the science of amethyst's colour, why it can fade in sunlight, how amethyst becomes citrine, and where the name comes from.
Khambhat: 4,500 years of Indian agate and carnelian
The Gujarat town that has cut agate and carnelian since the Harappan era: the Ratanpur mines, heat-treating carnelian, and beads that reached Mesopotamia.
Rainbow moonstone isn't quite moonstone
What rainbow moonstone really is, the difference between adularescence and labradorescence, why the black lines inside are a good sign, and where it comes from.
How a star gets into a ruby
Asterism explained: the rutile needles that put a six-rayed star in star ruby and star sapphire, how the stones are cut to show it, and how to see it best.
How a crystal sphere is made
From rough block to polished ball: how crystal and stone spheres are sawn, ground and polished, why some stones make better spheres than others, and what to look for.
Glass, dye and heat: an honest guide to what's natural
Opalite, goldstone, cherry quartz, dyed howlite and heated citrine: which popular 'crystals' are man-made or treated, and how to tell.