A few centuries ago, a phenomenon within some gems was figuratively described as ‘Folia.’ Taken from the Latin, meaning ‘Leaves’, this described the visible layering of crystals within a gem's structure: Today, this structure is known as cleavage. This leaf-like layered formation, occurring within a gem during its re-crystallization, happens by the process of applied one-directional pressure from the surrounding host rocks. This causes platy, or lengthened crystals to grow with their long axis perpendicular to the direction of the exerted force. Imagine the wind blowing from one direction on a field of long grass, then reproduce the image thousands of times over, layered one on top of the other.

Because the pressure forms the crystals structure to lie in one directional plane, it creates a plane of cleavage, making the rock brittle. Slate is a good example of ‘Foliated’ rock having a strong cleavage, while marble which has had pressure exerted on it from all sides during its formation is a good example of ‘Non-Foliated’ rock. The cleavage defines how the rock should be cut: ‘Foliated’ rocks have to be cut perpendicular (at right angles) to their line of cleavage otherwise they will break in splinters, whereas as a ‘Non-Foliated’ can be cut at all angles.

The objective of a good cutter is to optimize a gems beauty, desirability and value. A good, well-proportioned cut will bring out the true potential of a Tanzanite. Paramount is the skill of the cutter and his knowledge of positioning and angling facets, so light reflects internally to produce what is termed ‘Maximum Brilliance’.

Tanzanite at the blue end of the trichoic spectrum commands much higher prices than the purple or red tinged end. To pronounce the blue coloration a cutter must orientate the facets in conjunction with the blue color axis, which runs along the width rather than the length of the crystals axes. Cutting along the width axes will waste more of the Tanzanite rough crystal therefore augmenting the price per carat.