CONCHOIDAL
FRACTURE
OF OPAL

WHAT IS
FRACTURE?

Fracture is a description of the way a mineral tends to break. It is different from cleavage and parting which are generally clean flat breaks along specific directions. Fracture occurs in all minerals even ones with cleavage, although a lot of cleavage directions can diminish the appearance of fracture surfaces. Different minerals will break in different ways and leave a surface that can be described in a recognizable way. Is the broken area smooth? Irregular? Jagged? Splintery? These are some of the ways of describing fracture.

Although many minerals break in similar ways, some have a unique fracture and this can be diagnostic.

The most common fracture type is conchoidal. This is a smoothly curved fracture that is familiar to people who have examined broken glass. Sometimes described as a clam-shell fracture. Quartz has this fracture type and almost all specimens that have been broken, demonstrate this fracture type very well.
Another common type is subconchoidal. Similar to conchoidal, just not as curved, but still smooth. Andalusite can show this type.
Uneven is a type that is basically self explanatory. It is a common type that is found in anhydrite.
Unlike uneven, jagged has sharp points or edges that catch on a finger that's rubbed across the surface. Usually this indicates a metal such as copper , a metal alloy or some sulfides or oxides.
Splintery is a fracture type that occurs in fibrous or finely acicular minerals and in minerals that have a relatively stronger structure in one direction than the other two. Chrysotile serpentine is a typical mineral with splintery fracture and kyanite is an example of a non-fibrous mineral that has this fracture.
Earthy is a fracture that produces a texture similar to broken children's clay. It is found in minerals that are generally massive and loosely consolidated such as limonite.

OTHER PROPERTIES:

WHAT IS FRACTURE?

OTHER PROPERTIES:

WHAT IS
FRACTURE?