Elite: Dangerous - How to find Void Opals
What you need: surface scanner, cargo racks, a prospector limpet controller, a collector limpet controller (or multiple), a shield, abrasion blasters, a seismic charge launcher, a GOOD pulse wave analyser. A fast ship is preferable as well (when searching for the asteroids you want to go fast and not to waste time).
Step 1: Find a system with (pristine) icy rings; https://eddb.io is your friend for this task.
Step 2: Scan the rings with a surface scanning probe (not shown in the video, as I've already been to this location before).
Step 3: Fly to a Void Opal hotspot, but do not aim for the middle (aim a few hundred KMs away from the hotspot marker).
Step 4: Fly a good deal above / below the asteroid plane and spam the scanner.
Step 5: Identify core asteroids from a distance - if you're sufficiently far away only very likely asteroids will light up. Additionally all core asteroids are of the same shape; rather "uneven" and "messy".
Step 6: Confirm an asteroid is a core asteroid by looking for fissures (these are visible with the naked eye when using the night-vision mode) + use a prospector limpet to make sure the asteroid has a Void Opal core.
Step 7: Break them down: two high-yield charges in low-strength fissures should net the perfect detonation yield. If the yield is too strong, disarm one of the charges and find a medium-sized fissure to put a high-charge in instead.
Step 8: Boom!
Step 9: Collect + break chunks with the abrasion blasters.
Step 10: Cash out!
PS. The 7 extra Void Opals I get after I sell the initial batch are from the filled up hoppers in my refinery.