Mechanical properties of the principal rock-forming minerals of the Khibiny apatite — nepheline deposits

Conclusions

This elastic properties of minerals depend on structural elements (continuous chains, bands, framework structure), and the strength properties also depend on the nonuniformity of the structure (cleavage, joints, inclusions); fracture takes place at the surfaces of these nonuniformities. The maximum values of the strength properties of minerals without cleavage (apatite and nepheline) coincide with the direction of the maximal strength properties, namely. [001]. A similar regularity isobserved for aegirite—diopside because its most pronounced cleavage is not exhibited in the principal crystallographic directions. Microcline—perthite with maximal elastic properties in the [010] direction has minimal tensile strength in this direction, because perfect cleavage is observed in the latter. Inclusions in the crystals promote local stress concentrations and more rapid fracture; higher strengths are therefore observed for crystals with few or no inclusions.

Anisotropy of the strength properties is most marked (up to 60%) for minerals with poorer symmetry and more developed cleavage (microcline—perthite and aegirite—diopside).

For the minerals investigated a linear dependence is observed between the stresses and deformation up to fracture. For monomineralic aggregates the appearance of plastic deformations is observed at loads usually amounting to 30–70% of the breaking loads, owing to an increase in the number of nonuniformities in the rocks and to the sharp outlines of the grains of these aggregates. This also explains why the indices of the mechanical properties are lower than those of single crystals by a factor of 1.5–3.

The mechanical characteristics of the minerals enable us to assess the properties of the corresponding monomineralic aggregates and to establish the dependence of the properties of the rocks on the mineralogical composition.