Coconino Lapidary Club






Fracture in mineralogy is the texture and shape of the surface formed when the mineral is fractured. Fracture differs from cleavage and parting, which involve clean splitting along a plane surface, as it produces rough irregular surfaces [Ref1]. The appearance of fracture surfaces among minerals is highly varied and is a useful tool in identification. In this part of my Blog I’ll describe the fracture surfaces broadly seen in minerals.

Conchoidal fracture is characterized by smoothly curving nested arcs as those on a  seashell[Ref2].

Figure 1. Conchoidal fracture in rose quartz[Ref3,4].

Earthy fracture results in dull, clay-like surfaces without crystalline appearance[Ref2].

Figure 2. Earthy fracture in massive limonite[Ref5,6].

Fibrous fracture is typified by elongated crystal forms[Ref2]. 

Figure 3. Fibrous fracture in chrysotile (asbestos) [Re7,8].

Granular fracture is produced in aggregates of crystals[Ref2].

Figure 4. Granular fracture in an aggregate of arsenopyrite crystals[Ref9,10]

Hackly fracture produces torn edges and surfaces[Ref2].

Figure 5. Hackly fracture in copper producing torn edges[Ref11,12].

Irregular fracture presents an irregular fracture pattern[Ref2]

Figure 6. Plagioclase feldspar showing an irregular fracture surface[Ref13,14].

Splintery fracture produces thin long cleavages or partings[Ref 2].

Figure 7. Splintery fracture in actinolite [Ref15,16].

Uneven fracture features flat surfaces in a random pattern[Ref2].

Figure 8. Flat surfaces unevenly arrayed on blue sodalite[Ref17,18].


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