Tanzanite Grading and Clarity

tanzanite cushion cut Tanzanite Clarity Information and "Type" Grading

Any discussion of tanzanite gems would be remiss if it did not include information regarding clarity grading of the different types of gemstones found in nature. We discuss the 4 C's in the second section. The issue of gemstone clarity is best summed up as follows:

"There is hardly a gemstone which is completely "clean." Most of the time, they contain foreign matter or some kind of dislocation or irregularity in the crystal lattice. Sometimes only under the microscope can these "flaws" be discovered. In the lingo of the trade, one does not speak of flaws, but rather of inclusions, because the term flaw has a derogatory meaning that is not justified.

Since inclusions are not accidental appearances but rather are subject to strict conformities with natural law, they can tell a lot about the origin of the gemstone deposits and, in addition to that, they help in their identification. Even though each gemstone has its individual inclusion history, there are nevertheless forms of inclusions which can be grouped together and can be associated with specific gemstone types and/or gemstone imitations."

(excerpted from Gemstones of the World, pg. 49, Schumann; Amazon $24.95)

Schumann's excellent presentation on gemstone clarity and inclusion is worth the price of the book in and of itself and we highly recommend this book for your personal gemstone library. The book is thoroughly readable and is a valuable tool because of the information it contains.

Schumann alluded to gemstones being "grouped together" in terms of clarity and the following chart helps to understand this grouping a bit better by gemstone types:

Type
Description
Examples
I
Gemstones that normally occur in nature without inclusions. Tanzanite, Topaz, Aquamarine
II
Gemstones that normally occur in nature with a minimal amount of inclusions. Sapphire, Spinel
III
Gemstones that normally occur in nature with a moderate amount of inclusions. Emerald, Rubellite Tourmaline

GIA Colored Stone Clarity Grades - Eye Clean, Slightly Included, Moderately Included, Heavily Included, Severely Included.
Type 1
Type 2
Type 3
Eye clean - appears clean to the unaided eye.
Eye clean - appears clean to the unaided eye.
Eye clean - appears clean to the unaided eye.
Slightly included - minute inclusions difficult to see with the unaided eye.
Slightly included - minor inclusions easy to see with the unaided eye.
Slightly included - noticeable inclusions apparent to the unaided eye.
Moderately included - minor inclusions somewhat easy to see with the unaided eye.
Moderately included - noticeable inclusions apparent to the unaided eye.
Moderately included - obvious inclusions very apparent to the unaided eye.
Heavily included - prominent inclusions that have a negative effect on appearance or durability.
Heavily included - prominent inclusions that have a negative effect on appearance or durability.
Heavily included - prominent inclusions that have a negative effect on appearance or durability.
Severely included - prominent inclusions that have a severe effect on appearance or durability or both.
Severely included - prominent inclusions that have a severe effect on appearance or durability or both.
Severely included - prominent inclusions that have a severe effect on appearance or durability or both.

The key to understanding clarity in tanzanite is that it most commonly occurs free from inclusions, so when it is graded under 10x magnification, very rigid guidelines are present for a stone to be considered flawless or nearly so.

Not so is the case with emeralds. They normally occur in nature with a moderate number of inclusions, therefore as a Type III stone the clarity scale is re-defined to compensate for this difference.

In summary, different Types (I, II, III) of gemstones should be compared to their peer group of stones before determining value. From the above chart, a slightly included Type III stone will appear more included than a slightly included Type I stone. Please let us know if you have any questions on this concept.

Tanzanite Pear Shape