Final answer:
The substance being referred to is calcite, particularly the Iceland spar variety, known for its optical properties and potential to display phosphorescence or fluorescence. These characteristics are due to the specific atomic energy levels in minerals that allow them to emit light.
Step-by-step explanation:
The substance being described is likely to be calcite, which can appear transparent to opaque and may sometimes exhibit phosphorescence or fluorescence. A notable transparent variety of calcite is known as Iceland spar, and it has significant optical uses due to its ability to polarize light.
Fluorescent substances, like certain minerals, can absorb light energy and re-emit it, which explains why some rocks glow under a UV lamp or a black light. This is due to the atomic energy levels within the mineral, with the emitted color being dependent on the mineral's composition.
Similar properties apply to phosphorescent materials, which can maintain excited energy states and release them slowly as visible light.
In relation to optical qualities, a high-quality diamond may appear clear and colorless but can sparkle brilliantly when illuminated due to its ability to disperse light into various colors—a process enhanced by its faceted structure.
The effects of fluorescence and transparency are often manipulated in various fields, including microscopy, to enhance contrast and resolution, or in art to create works that glow under specific lighting conditions.