Editing Kimberlite (section)

=== Group I kimberlites ===

Group-I kimberlites are of CO<sub>2</sub>-rich [[ultramafic]] potassic igneous rocks dominated by primary [[Forsterite|forsteritic olivine]] and carbonate minerals, with a trace-mineral assemblage of magnesian [[ilmenite]], chromium [[pyrope]], [[almandine]]-pyrope, chromium [[diopside]] (in some cases subcalcic), [[phlogopite]], [[enstatite]] and of Ti-poor [[chromite]]. Group I kimberlites exhibit a distinctive inequigranular texture caused by macrocrystic ({{convert|0.5|-|10|mm|in|disp=or|abbr=on}}) to megacrystic ({{convert|10|-|200|mm|in|disp=or|abbr=on}}) phenocrysts of olivine, pyrope, chromian diopside, magnesian ilmenite, and phlogopite, in a fine- to medium-grained groundmass.<ref>{{Cite journal |last1=Sarkar |first1=Soumendu |last2=Giuliani |first2=Andrea |last3=Dalton |first3=Hayden |last4=Phillips |first4=David |last5=Ghosh |first5=Sujoy |last6=Misev |first6=Sarah |last7=Maas |first7=Roland |date=2023-06-20 |title=Derivation of Lamproites and Kimberlites from a Common Evolving Source in the Convective Mantle: the Case for Southern African 'Transitional Kimberlites' |url=http://dx.doi.org/10.1093/petrology/egad043 |journal=Journal of Petrology |volume=64 |issue=7 |doi=10.1093/petrology/egad043 |issn=0022-3530|hdl=20.500.11850/623387 |hdl-access=free }}</ref>

The groundmass mineralogy, which more closely resembles a true composition of the igneous rock, is dominated by carbonate and significant amounts of forsteritic olivine, with lesser amounts of pyrope garnet, Cr-[[diopside]], magnesian ilmenite, and [[spinel]].