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Fracture
is the way a mineral breaks other than along cleavage
planes and is described in terms of the shapes resulting
from the fracture of the material. The most distinctive
type of fracture is conchoidal (shell like) which
results in concentric concave ridges. This is the common
type of fracture in glass type materials such as Obsidian.
Quartz,
Opal
and Peridot
also break with conchoidal fracture (in other than cleavage
directions).
Types of fracture are:
- Conchoidal (shell like) which
results in concentric concave ridges
- Subconchoidal,
which is similar to conchoidal but less prominant, often
lacking the concentric ridges.
- Even.
A fairly smooth, flat break that may visually resemble
a cleavage plane.
- Granular.
A fine-grained break resembling the surface of
a sugar cube.
- Spintery.
A fibrous break that resemles splintered wood.
- Uneven.
A general catagory used to describe fractures with an
irregualr appearance such as aggregate gem materials
like Serpentine.
- Steplike.
Breaks that may be a combination of cleavages in more
than one direction or a combination of cleavages and
fractures.
Fracture,
along with cleavage,
can be of important diagnostic value in determining
a type of unknown mineral.
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