Quality and Mineralogical Evaluation Principles of Opal (Opal) for Deposition and Gemological Sciences

# # Quality and Mineralogical Assessment Principles of Opal (Opal) for Deposition and Gemological Sciences

Opal is an amorphous mineral with no crystal structure. There is a chemical formula, SiO2.nH2O, composed of silicon dioxide and water. With about 3 to 21 percent of the water content accumulated inside the structure. Opal is caused by the precipitation of silica solution in the cracks of the rock. In the water evaporates with time, silica will form a small, orderly aligned sphere. The diffraction of light through this alignment gives rise to Opal's unique play-of-color phenomenon.

# # # Quality metrics and hierarchy for accumulation

In the cumulative quality assessment, there are important indicators: Play-of-Color, Cleanliness, and Cut Quality. The quality level is classified as follows:

* * * AAA Level: * * Ultimate Opal Bright Color Play, Unblemished & Perfect Uncut Suitable for Luxury Jewelry and as Masterpiece Collectible Workpiece

* * * AA level: * * There is good color play, but the color intensity is reduced. There may be a slight blemish. The cut is still good.

* * * Level A: * * Light Color Play Cleanliness is getting clear. Popular for use in affordable jewelry.

* * * Level B: * * Basic Quality Light Color Play No Contrast To Uncut Suitable For Crafts Or Practice Work

# # # Cumulative and Rare Levels

The cumulative attractiveness of opal is determined by the brightness of the color play, pattern patterns, especially the rare and desired table patterns (Harlequin) from collectors.

Black Opal is a rare type. White Opal and Crystal Opal are common.

# # # Average prices in the current market

The price of opal varies by grade:

* * * Grade B: * * Starting price from 300 to 1,500 baht per carat

* * * Grade A and AA: * * Average price from 2,000 to 15,000 baht per carat

* * * AAA grade: * * Prices start from THB 50,000 to Millions depending on the satisfaction of the collector.

# # # Mineral Stability and Storage (Stability & Care)

Stability is an important factor for opal deposition, in that if stored in a dry and overheated environment, it causes cracking (Crazing), collectors should therefore understand the physical properties of the ore, including preventing temperature and chemical changes.

Store pawn collection by Bunchong Tientong

7 Mar 2026