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How to grade a mineral

Minerals are works of art, each mineral is totally unique and can be judged by a multitude of criteria. Some criteria are subjective (in the eye of the beholder), while others can be quite concrete. This grading system is a guide designed to help collectors assess how any given specimen ranks among its peers.

As a guide, it provides reference points while still leaving open the possibility that a specimen can be beautiful and treasured simply due to the fact that you enjoy its appearance or that it moves you.

It is here that the worlds of art and nature meet.

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How Our Grading System Works

There are two sections to the guide: Section A with five criteria, and Section B with four criteria.

Each individual criteria is graded out of ten, ten being the best possible and most desirable score. Add up all nine criteria and then divide that sum by nine. This will give you an average score.

Of course there are some specimens where specific criteria are not applicable. In those cases, add up your individual criteria scores, then divide by the number of criteria used to get to your average score.

Please note that this guide is to help collectors assess their collections. A high score does not necessarily denote a high monetary value.


Average Scores

9-10 - Exceptional quality

8-8.9 - Very good quality

7-7.9 - Good quality

6.9 > - Not of collectible quality

Section A

Focuses on the quality of the crystal

Section B

Focuses on the quality and relationship between both the crystal and the matrix

V. Crystal Size

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Wilensky Approach

Crystal Size

This criterion can be significant. In the mineral kingdom, large and perfect crystals are valued due to rarity in relation to smaller examples. A large crystal in and of itself is not significant. This criterion is only for large crystals that are equal or superior to smaller examples of the same mineral. For example: an aquamarine crystal that is two inches tall, gem clear, top color, and on a beautiful matrix is less important than one of exactly the same quality that is eight inches tall. Superb two-inch-tall aquamarines are not uncommon. However, eight-inch-tall examples are very rare. This criterion becomes more important in species that are rarely found in large sizes. We also limit this criterion due to the fact that not all collectors want larger specimens.

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