Ultra realistic geological photograph, 9:16 vertical. Inside a vast underground cave covered in enormous natural selenite crystals. A single shaft of sunlight refracts into rainbows. MATERIAL PHYSICS — SELENITE CRYSTALS: Giant selenite (gypsum) crystals — naturally formed over hundreds of thousands of years in supersaturated mineral water. The crystals are translucent white with subtle amber and honey-gold inclusions from iron impurities. The largest crystals are 6 feet long and 1 foot in diameter — massive hexagonal prisms with flat termination faces and striated side faces showing growth lines. Smaller crystals (1-3 feet) cluster around the bases of the larger ones. The crystal surfaces are NOT smooth glass — they have visible growth striations running lengthwise (parallel lines from sequential mineral deposition), small imperfections where crystal faces intersect at slight misalignment, and the occasional inclusion of darker mineral trapped during growth as a shadow visible inside the translucent body. The crystals cover every surface — floor, walls, and ceiling. On the ceiling they hang downward like a forest of glass stalactites. On the floor they grow upward like a crystal garden. On the walls they project outward at various angles following geological fracture lines. THE LIGHT SHAFT: A single narrow shaft of white sunlight enters from a crack in the cave ceiling approximately 80 feet above. The beam is visible as a solid-looking column of light in the slightly dusty cave air. Where the beam hits a large crystal cluster at the cave center, the light enters the crystal and REFRACTS — exiting as multiple beams of spectral color. Rainbow caustic patterns are projected onto the cave walls and floor — patches of red, orange, yellow, green, blue, and violet scattered across the crystal surfaces. The refraction is physically accurate — the beam separates into its component wavelengths at the crystal face angle. MATERIAL PHYSICS — CAVE FLOOR: Shallow pools of still water cover portions of the cave floor — the water is mineral-saturated and crystal clear. The pools reflect the crystals above as distorted inverted images. Small new crystals are growing in the pools — tiny transparent formations indicating the cave is still geologically active. CAMERA: Nikon Z8, 14mm f/1.8 at f/8, ISO 400, tripod. The extreme wide angle captures the cathedral-scale of the cave. LIGHTING: The single sun shaft is the only light. Where it hits and refracts, the cave is illuminated in prismatic color. Where it doesn't reach, the cave fades to dark blue-grey — the crystals in shadow are visible as dim translucent shapes with a faint glow from transmitted ambient light. NEGATIVE PROMPT: people, miner, tourist, artificial light, flashlight, cartoon, CGI, text, watermark, small cave.