Usually hard but brittle
Ionic or covalent

Ionic

Explanation:  Ionic compounds tend to be hard and brittle while covalent compounds tend to be softer and more flexible.

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in cartography, a contour line (often just called a "contour") joins points of equal elevation (height) above a given level, such as mean sea level. a contour map is a map illustrated with contour lines, for example a topographic map, which thus shows valleys and hills, and the steepness or gentleness of slopes.

explanation: