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Oxides
T
he oxide class of minerals, in a strict sense, encompasses over 90 percent of all minerals
on earth. For simplicity, mineralogists have limited the class to only the non-complex
subclasses containing oxygen and hydroxide. Oxides contain ionic bonds
which distinguish them from members of the more complex mineral classes. The
oxide class is very diverse, including minerals that are at the highest and lowest
ends of the hardness scales. The diversity is due to oxygen making up 45 percent of the
earth's crust. They are compounds of one or more metallic elements combined with
oxygen, water, or hydroxyl (OH). The minerals in this group contain the greatest
variations of physical properties. Some are hard, some soft. Some have a
metallic luster, while others are clear and transparent.
Spinel images courtesy of theimage.com
The oxides can be divided into three groups:
- Simple Oxides - Compounds of metallic elements combined with oxygen, including
such minerals as corundum and hematite. Rubies and sapphires are of the corundum
group.
- Hydroxides or Hydrous Oxides - Compounds of metallic elements combined with
water (H2O) or hydroxyl (OH).
- Multiple Oxides - Compounds of two different metallic elements combined with
oxygen, like chrysoberyl and spinel.
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