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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

ii. Transparency

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Wilensky Approach


This criterion only applies to those species which are transparent. It also considers varying degrees of transparency from “water clear” to opaque, within the context of what is known about the specific species. Any species not commonly found clear is far more valuable in crystals that are. The commonly used term “gem” or “gem-quality” implies the piece has a gem like appearance, which is the highest form of transparency and the most sought after in all species. The property of a solid object being transparent has for millennium intrigued and fascinated humans. We are drawn to objects that glow. The light shining through a crystal should create a luminescent glow.

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