When you light up a shard of clear material, such as quartz or glass, and it produces a crackling sound, it usually indicates the presence of thermal stress or a phenomenon called thermal shock. Here's an explanation of what might be happening:
Differential Expansion: Clear materials like quartz or glass have relatively low thermal conductivity, meaning they don't conduct heat well. When you expose a shard of clear material to intense heat, such as an open flame, it heats up quickly at the point of contact.
Uneven Heating: As the shard heats up, different parts of the material expand at different rates due to variations in temperature. If the heating is uneven or concentrated in one area, it can cause localized expansion.
Thermal Stress: The uneven expansion leads to the development of thermal stress within the material. When the stress exceeds the material's capacity to withstand it, small cracks or fractures can form.
Crackle Sound: The crackling sound you hear is the result of these small cracks propagating and releasing stress as the shard heats up. The cracks can create a popping or crackling noise as they propagate through the material, sometimes accompanied by visible signs like small sparks or glowing.
It's important to note that subjecting clear materials to rapid and extreme temperature changes, such as heating them directly with a flame, can lead to thermal shock and potentially cause the material to break or shatter. To avoid this, it's generally recommended to heat clear materials gradually and evenly, allowing them to adjust to temperature changes more smoothly.
If you encounter a crackling sound when heating a clear shard, it's advisable to exercise caution and ensure proper safety measures are in place.