What is a material more easily cut than shattered?
The crystalline property that would allow to cut the &quot;diamond creature&quot; (or whatever those things are in your universe) you are looking at is cleavage (a writer might also use a term in a wordplay).
In crystallography, cleavage is the ability of crystals to crack or split in certain crystallographic directions.
This mechanical property of crystalline media is associated with their internal structure (the ratio of adhesion forces in the crystal lattice) and does not depend on the external shape of the crystals.
This property is also often utilized in the beginning of the process of fashioning the gemstones.
There is a fascinating demonstration with explanation: Crystals - Alan Holden 1958 (YouTube).
With diamonds you can do that too, just not always as easily as with mica: Diamond Cleavage (YouTube).
Diamond (as well as ﬂuorite, galena, topaz and some other minerals) possesses a so-called &quot;perfect&quot; cleavage, and the cleavage planes in diamond are parallel to the octahedral crystal faces [1, p. 30]:


Figure 4.1 Two examples of directional-dependant properties in diamond. The cleavage planes are parallel to the octahedral faces, which are also planes of near
maximum hardness. The easiest direction for sawing is at right-angles to the dodecahedral plane, which is also the plane of minimum hardness.

References

Read, P. G. Gemmology, 3rd ed.; Elsevier Butterworth Heinemann: Amsterdam; Boston, 2005. ISBN 978-0-7506-6449-3.