Fluorite

It cleaves in four directions at once.

Mohs 4, which means a steel nail marks it and any quartz point will carve your name into it. It cleaves in four directions at once. A light knock takes off a clean triangular flake. Derbyshire's Blue John was mined by the Romans and still fades in a sunny window.

There is no putting it back.

Calcium fluoride at Mohs 4, coloured every shade in the box by defects in its own lattice. Derbyshire's Blue John has been mined since the Romans and there is very little left. It cleaves in four directions, so a knock takes off a clean triangular flake. There is no putting it back.

Fluorite gave fluorescence its name.

Fluorite gave fluorescence its name, and Derbyshire's Blue John has been coming out of the same hill since the Romans. A steel nail scratches it, which separates it from every purple quartz on the shelf in one stroke. Never heat it, because hot fluorite gives off hydrogen fluoride.

A light knock splits it clean along four planes.

Perfect cleavage in four directions means a light knock splits it along a flat plane and nothing can be done afterward. Derbyshire's Blue John has come out of the same hill since the Romans. It fades in sun and cracks with temperature change, so keep it somewhere stable.

Fluorescence was named after this mineral.

Fluorescence was named after this mineral. Calcium fluoride, grown as cubes and octahedra banded in straight-edged zones of purple and green, and Derbyshire's Blue John has been worked since the Romans. Four directions of perfect cleavage. One knock splits it clean along a triangle.

The mineral that gave fluorescence its name.

A steel knife cuts it, which separates fluorite from every purple and green quartz in the shop in one pass. Four perfect cleavage directions mean a light knock splits it along an octahedral plane. It is the mineral that gave fluorescence its name, and Derbyshire has mined Blue John since the Romans.

Purple against green with no blending between them.

Calcium fluoride, and the mineral the word fluorescence was named after. It cleaves perfectly in four directions, so a knock produces flat triangular facets rather than a chip, and the colour arrives in hard straight bands following the growth planes. Purple against green with no blending between them.

A light knock splits it along four planes at once.

Calcium fluoride, and the mineral that gave fluorescence its name after specimens from Derbyshire glowed under early experiments. It cleaves perfectly in four directions at once, so a light knock takes a triangular flake straight off it. Do not heat it, because hot fluorite can release hydrogen fluoride.

The word fluorescence is named after this mineral.

The word fluorescence is named after this mineral, which glows blue under a UV torch and cleaves into triangles if you drop it. Derbyshire's Blue John variety has been worked since the Romans. A steel knife scratches it, which separates it from every purple quartz on the shelf.

A light knock splits it and hands you a triangle.

Four directions of perfect cleavage, so a light knock splits it along a plane and hands you a triangle. It gave fluorescence its name, and Derbyshire has been pulling the Blue John variety out of the ground since the Romans. A steel knife settles any argument about what it is.

Fluorescence was named after this mineral, not the reverse.

Fluorescence was named after this mineral, not the reverse. Calcium fluoride in cubes and octahedra, with four directions of perfect cleavage, so a light knock takes a corner off cleanly. Never heat it, since hot fluorite can release hydrogen fluoride.

The bands are stacked in the order they arrived.

Four directions of perfect cleavage mean a knock takes a clean corner off rather than chipping. The straight-edged colour bands are growth zones, purple against green against clear, stacked in the order they arrived. Prolonged sun weakens the colour and heat can crack it outright.

Fluorite is carried for clarity, calm and boundaries. Calcium fluoride in cubes and octahedra, coloured every shade in the box by lattice defects and trace elements, and the mineral that gave fluorescence its name.. Tradition links it to the third-eye, throat, heart chakra.

Fluorite is not faked often, but it is still worth checking. A steel knife or nail scratches fluorite (4) but not quartz (7), this single test separates it from every purple and green quartz on the shelf. Look also for triangular cleavage facets and blue fluorescence under a UV torch.. Untreated in most cases.

A short rinse is fine for fluorite, then dry it. Keep it out of direct sun, because the colour fades and does not come back.