**3. The heterogeneous composition of Mg-ilmenite macrocrysts**

Most Ilm grains are heterogeneous, with rims enriched in MgO. The Ilm zonal megacrysts are illustrated in **Figures 7** and **8**, in which the rims are enriched with MgO. The gradual change in the primary composition of Ilm is especially clearly observed in polygranular megacrysts from the Mir pipe (**Figure 9**). Individual granules ranging in size from 100 μm to >1 mm, separated by microcracks, demonstrate a compositional change towards an increase in MgO content from the center to the edge (**Figure 9a, b, e, and f**). At the same time, there is a parallel decrease in the content of

### **Figure 7.**

*Typical zoning of Ilm macrocryst: The marginal zone of the grain becomes more magnesian than the core. In the photo, the microcrystal Ilm from the kimberlite of the Malokuonamskaya pipe (Kuranakh field). Zoning: in the center (point 1) 5.16% MgO, 0.72% Cr2O3; In the rim (point 2) -11.8% MgO, 2.8% Cr2O3.*

### **Figure 8.**

*Macrocryst Ilm from the kimberlite of the Universitetskaya pipe (Kuranakh field). In the center, relicts of high-Fe, low-Cr Ilm (point 1) are preserved, most of the grain is recrystallized in relatively high-Mg, high-Cr Ilm. Composition: Point 1 5.7% MgO, 0.4% Cr2O3; point 2–10.6% MgO, 1.5% Cr2O3; point 6–9.6% MgO, 0.9% Cr2O3.*

### **Figure 9.**

*(a) Uneven granulation of Ilm macrocryst. The formation of microcracks on the boundaries of granules. (b) the changing of Ilm composition is starting in the border zones of granules. (c) relatively uniform micro granulation of Ilm grains with the size of individual granules of 100–200 mμ. (d) Development of microcracks (granulation process) throughout the macrocrystal Ilm, accompanied by a change in composition on only one-half of the grain. (e, f) - The more intensive development of the processes of granulation and substitution takes place in linear microzones of fracturing.*
