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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.

Download Wilensky Approach 

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

iv. Perfection

Back to Criteria
Wilensky Approach


This criterion relates primarily to the physical condition of the specimen and its lack of damage or appearance of damage. We often say that if it looks like damage, then it is damage. There are different kinds of damage: “Wilbur’s” (named after one of America’s greatest mineral collectors, and our good friend, Dave Wilbur – not because his minerals had “Wilbur’s”, but rather because they did not), dings, nicks, breaks, and cleaves on a crystal or matrix. Damage is part of the reality of collecting minerals as very few are truly perfect.


Damage, which are noticeable and interrupt the beauty of a specimen, are not acceptable. Often, a crystal will have what is known as a contact. Contacts are where a crystal was up against, or grew next to, another crystal or matrix. This is natural and as long as they are not unsightly is acceptable.


This criterion also includes repair and restoration. We believe that repair and restoration are acceptable when it is invisible, nearly invisible, does not impact the beauty or aesthetics of a mineral, or when the specimen is considered the finest or among the finest known examples. This must be considered when assessing specimens that are considered so magnificent, rare, and important that repair and restoration is unavoidable to preserve a specimen of great significance.

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