the tough natural covering of some organisms | a protective cover that protects the face of a watch |
a covering that is intend to protect from damage or injury | glassware made of quartz |
| a crystalline element used as a component in various electronic devices |
| a rock formed by the solidification of a substance; has regularly repeating internal structure; external plane faces |
| a solid formed by the solidification of a chemical and having a highly regular atomic structure |
| colorless glass made of almost pure silica |