Minerals What is a mineral? Solid Cannot be a liquid or a gas Naturally occurring Cannot be man-made Inorganic Cannot be the result of a living thing What is a mineral? Fixed composition Must be made of specific chemicals in specific ratios Most are compounds, some are only elemental like gold Crystalline structure Form specific geometric shapes because of the arrangement of the atoms it contains (crystals) Is this a mineral? How minerals form Magma cooling inside the earth Forms large crystals because of the amount of time it takes to cool Lava cooling quickly on the surface of the earth Usually forms smaller crystals because of the rapid cooling time How minerals form Elements and compounds dissolve in water When the water evaporates, we are left with the minerals Identifying minerals Color Some minerals have the same color, so this is the least accurate way to identify minerals Identifying minerals Streak The color of the powder left behind when scraped on a piece of glass or porcelain Identifying minerals Luster How the mineral reflects light The main 2 lusters are metallic and non- metallic Identifying minerals Some other ways to describe luster are: Dull - just a non-reflective surface of any kind Earthy - the look of dirt or dried mud Fibrous - the look of fibers Greasy - the look of grease Gumdrop - the look a sucked on hard candy Metallic - the look of metals Pearly - the look of a pearl Pitchy - the look of tar Resinous - the look of resins such as dried glue or chewing gum Silky - the look of silk, similar to fibrous but more compact Submetallic - a poor metallic luster, opaque but reflecting little light Vitreous - the most common luster, it simply means the look of glass Waxy - the look of wax Identifying minerals Cleavage and fracture ( The way a mineral breaks) Cleavage means to break along flat planes Fracture means to break in irregular pieces Cleavage Fracture Identifying minerals Hardness How easily a mineral is scratched We use the Mohs Hardness Scale to compare Identifying minerals Density Density = mass volume Most minerals will have different densities Identifying minerals Crystal structure We classify minerals by the angles and numbers of crystal faces a mineral has. Identifying minerals Fluorescence Some minerals will glow in UV light Identifying minerals Magnetic Some minerals will attract metals like a magnet Identifying minerals Reacts with acids Some minerals will bubble and decompose when exposed to acids REMEMBER Some (Streak) Llamas (Luster) Climb (Color) Down (Density) Funny (Fracture/Cleavage) Hills (Hardness)