Tanzanite Shopping Guide
Rated with a hardness of 6.5 – 7 on Moh’s hardness scale (for comparison, diamond, the hardest mineral, is rated 10), tanzanite should be carefully looked after. Even though tanzanite is better suited to earrings and pendants as a result of its softness, a suitable setting in a dress ring and careful maintenance will give years of pleasure to a discerning owner.
Cut refers to the shape, facets and proportions of a tanzanite. The quality of the proportions of a cut tanzanite will significantly affect the resultant brilliance of the stone. A ‘fine’ cut ensures that the stone’s facets reflect light to create maximum brilliance. Tanzanites are cut into a variety of shapes, predominantly determined by the shape and size of the rough crystal form.
Colour refers to the blue in tanzanite and its degree of violet saturation. The predominance of either blue or violet in a stone is indicated by “B” or “V” respectively. The depth of colour, or saturation, of tanzanite is varied and ranges from exceptional to pale. The deeper the colour of tanzanite, the more valuable it is.
The clarity of a tanzanite refers to the degree of natural flaws and inclusions within a polished stone. Polished tanzanite stones are graded under 10x magnification through a jeweller’s loupe and may range in clarity from Eye Clean to Heavily Included.
Stones that are classified as Eye Clean or Slightly Included contain inclusions that are not visible to the naked eye and as such do not detract in any way from the beauty of the stone. Larger inclusions lead to classification as either Moderately or Heavily Included and these may be seen by the naked eye. The more flawless (less inclusions) a tanzanite contains, the more valuable it is.
The majority of sapphires sold today have been subjected to heat treatment processes. Subjecting cloudy and poor quality sapphires to high temperatures improves the quality and intensifies the colour of these sapphires. The results of these heating processes are permanent and a treated sapphire will not deteriorate in colour or clarity over time. Such enhancement of sapphires has ensured that today, sapphires are more accessible and affordable than before. It has been estimated that only 1% of sapphires sold today have not been heat treated and these command prices far in excess of those paid for treated sapphires.