Mineral powder is powdered makeup made primarily of finely ground ingredients derived from natural minerals like titanium dioxide, zinc, mica, and iron oxides. However, it is not simply pure minerals found in their natural form and ground up. They are processed, but the ingredients are safer and gentler on the skin than many of the ingredients used in traditional makeup. Mineral powder is often suitable for people with sensitive skin, acne, and rosacea. It can provide different levels of coverage and can be found in matte, semi matte and dewey/luminous varieties.
Mineral powder makeup has several major benefits. The ingredients are generally safer and less likely to irritate the skin. It tends to look more natural on the skin than traditional makeup, and tends to stay on the face longer. It can be reapplied without looking heavy or cakey. It is easy to get sheer coverage for a "no makeup" look, but medium and full coverage can also be achieved by applying it in light layers. As long as the layers are thin and well-buffed into the skin, it creates a flawless look that doesn't look clumpy, mask-like or settle into lines and make them more visible. It also looks more natural in bright and unnatural light, and for this reason is often preferred for photo shoots.
Although some major cosmetic companies have gotten on the mineral makeup bandwagon and add all kinds of fillers, preservatives and other ingredients of questionable long-term safety, mineral cosmetics tend to have fewer fillers, preservatives and other ingredients the safety of which has been called into question. It would be a stretch to call mineral makeup all natural due to the processing of the mineral ingredients to produce it, but it can be made without the usual chemical additives and preservatives found in most traditional makeup.
Common ingredients include titanium dioxide, zinc oxide, mica, bismuth oxychloride, iron oxides, ultramarines, and boron nitride. Oil-absorbing ingredients such as silica, kaolin clay and rice powder are often included in matte formulas. Some ingredients, like zinc oxide and boron nitride, have anti-inflammatory properties, and often people with rosacea and acne find that mineral powder does not irritate their skin. People with sensitive skin sometimes find their skin is irritated by bismuth oxychloride and mica. Most matte foundations do not include these ingredients, since they give shimmer to the makeup. If your skin is sensitive or if you've had trouble with those ingredients in the past, you may want to stick with matte mineral makeup.
Mineral powder can be applied with any standard powder brush, with a damp sponge, or with the fingers when mixed with moisturizer. It's always applied in thin layers on the skin. For a sheer look, one layer may be enough. If you need fuller coverage, 2 or 3 layers can be applied. But it must be layered rather than applied in one heavy layer. Otherwise it will not blend into the skin properly and it will look unnatural, dry or clumpy.