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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

Wilensky Approach


How does the specimen compare in color to other known examples?  Vivid, bright, intense, and saturated in color are all positive qualities we want in a crystal. Typically, a more saturated and vivid color is more valuable and desirable. Minerals that are transparent can be less valuable if they are too dark and light does not transmit through the crystal. This criterion is somewhat relative, primarily due to the type of lighting when viewing the mineral. You will see differences in color when viewing specimens in daylight, incandescent light, halogen light, or fluorescent light. Color perception is directly related to lighting, but still measurable in relation to other known examples under the same lighting conditions.

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