| Webster's Online Dictionary |
| Expressions | Domain | Definition | |
| Blue needles | Mining | Applied in the grading of quartz crystals to needlelike imperfections, often definitely oriented, which show up with a bluish-white color under the carbon arc. The color is due to the selective scattering of blue light by the minute imperfections. (references) | |
Source: compiled by the editor from various references; see credits. | Top | ||
