Crystal care begins with mineral properties. Hardness predicts scratching, while toughness, cleavage, porosity and chemical stability answer different questions.
What the Mohs scale tells you
The Mohs scale compares which mineral can scratch another. Talc is 1 and diamond is 10, but the intervals are not equal. A quartz point at 7 resists ordinary scratches better than calcite at 3; that does not mean quartz cannot chip or fracture.
Selenite is a variety of gypsum and can be marked by a fingernail. Fluorite cleaves readily. Opal can contain water and respond badly to rapid temperature changes. The trade name on a shop label is not enough for care advice.
Light, heat and storage
Strong sunlight can fade minerals such as amethyst; heat and sudden temperature change can damage included or hydrated stones. Store pieces separately so harder minerals do not scratch softer ones, and support delicate clusters rather than lifting them by points.
Choosing a reference
Prefer mineralogical names, hardness ranges and specific cautions over universal “cleansing” lists. A useful book distinguishes physical maintenance from spiritual practice and never presents the latter as a substitute for material safety.
