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Science
Minerals
Opals
All Subcategories (25)
Appearance
Characteristics
Descriptions and features
Desirable Opals
Desirable qualities
Desirable quality
Opal Characteristics
Opal characteristics or Opal properties
Opal colors
Opal Mining
Opal qualities
Precious opals
Properties or Characteristics
Qualities
Rarity and Desirability
Types
Types of Opals
Types/Qualities of Opals
Value
Value and Price Determinants
Value and Rarity
Value of Opals
Varieties and characteristics
Varieties and Qualities
Visual Properties
Parent Categories (12)
Facts
Gems and Minerals
Gems or Minerals
Gemstones
Gemstones and Minerals
Geology and Minerals
Inferences
Minerals
Minerals and Gemstones
Minerals or Gemstones
Valuable resources
Valuables