Selenite

What causes the color: Colorless to white in its pure form; the transparency and pearly-to-vitreous luster come from its layered, fibrous or bladed crystal structure, which also produces the characteristic 'silky' sheen seen in fibrous selenite specimens (sometimes called 'satin spar').

How it forms: Forms in evaporite deposits — where ancient seas or saline lakes evaporated, concentrating calcium sulfate until it crystallized — often as large, well-formed crystals growing slowly in cavities within sedimentary rock or clay. The Cave of the Crystals in Naica, Mexico is an extreme example, with selenite beams over 10 meters long formed by slow crystallization in mineral-rich water at stable temperature over hundreds of thousands of years.

Treatments & imitations: Generally untreated and inexpensive enough that faking it isn't commercially common; occasionally confused with other soft white minerals or with cheap plaster/gypsum casts, though genuine selenite's fibrous, layered structure and characteristic soft sheen are distinctive once you know what to look for.

Real vs. fake: The fingernail-scratch test is the fastest genuine identification method: real selenite (Mohs 2) will show a visible scratch mark when you drag a fingernail (Mohs ~2.5) firmly across it. Plastic or resin imitations won't scratch this way and typically look too glossy/uniform compared to selenite's natural fibrous, slightly striated surface.

Historical use: Thin sheets of selenite (sometimes called 'lapis specularis' by the Romans) were historically used as an early form of window glass and lantern covering before glassmaking was widespread, since it splits into flat, translucent sheets. It has also long been used ornamentally in the Middle East and North Africa, carved into vases and decorative objects.

Metaphysical tradition: In modern crystal-healing tradition, selenite is widely used as a 'cleansing' stone — practitioners often place other crystals on or near a selenite slab in the belief it clears their energy, and use selenite wands in meditation for a sense of mental clarity and calm.

How to use it: Frequently kept as a flat slab or charging plate that other crystals are placed on, used as a wand for tracing over the body in energy-work practice, or displayed as a tower/point in a room. Because it's so soft, it's rarely worn as everyday jewelry the way quartz-family stones are.

Cleansing & care: IMPORTANT: selenite is water-soluble (it's a hydrous mineral, calcium sulfate dihydrate) and will dissolve, pit, or cloud if soaked or left wet — never clean it with water. Dust it with a dry, soft cloth instead. Its Mohs 2 hardness also means it scratches extremely easily, so store it separately from harder stones, and handle it more carefully than you would quartz-family crystals.