megacryst

megacryst

[′meg·ə‚krist]
(petrology)
Any crystal or grain in an igneous or metamorphic rock that is significantly larger than the surrounding matrix.
References in periodicals archive ?
The most common megacryst phase is plagioclase, followed by amphibole, all set in a fine-grained matrix (Fig.
In addition, both megacryst and ecologite paragenesis garnets are well-represented in this kimberlite.
The composition of the A15 megacryst garnets is similar to the megacrystic suite of the diamond-rich Jericho kimberlite of the Slave craton with both exhibiting a distinct reduced crystal chemistry, which is most promising for the stability and preservation of diamond.
Using this classification, 23 mantle-derived garnets were recovered: one (1) Harzburgitic or "G10" garnet, four (4) Lherzolitic or "G9" garnets, thirteen (13) catazonal garnets "G5", four (4) eclogitic garnets or "G3" and one (1) low-chromium megacryst or "G1".
Finally, a coarse muscovite grain from a quartz-feldspar-muscovite intergrowth surrounding a blocky K-feldspar megacryst was dated with the [sup.
Technical advances on the property last year include the recovery of G-9 pyropes and megacryst garnets that, together with other indicator minerals found in the preceding years, show a mainstream diamond source of likely eclogitic origin.
This dominantly monzogranitic pluton, generated by hybridization between mantle and crustal magmas, consists of mappable facies; end members range from less hybridized with high concentrations of very coarse K-feldspar megacrysts and abundant mafic microgranular enclaves, to more hybridized with low megacryst and enclave abundances.
A range of stages of development of massive crystalline aggregates is observed in the samples: individual microcrysts, framboids, framboid clusters, recrystallized megacryst overgrowths, and banded concentric zones.
A close-up photograph of the outcrop along McDougall Inlet clearly shows pink megacrysts of potassium feldspar with rapakivi mantling characteristic of the Jimmy Hill Granite in contact with the equigranular John Lee Brook Granite (Fig.
Age and origin of gem corundum and zircon megacrysts from the Mercaderes-Rio Mayo area, south-west Colombia, South America.
Underplating of Mesozoic mantle-derived magmas in Tongling, Anhui Province: evidence from megacrysts and xenoliths.
It is full of feldspar megacrysts (some over 7 cm long) in a granitic groundmass.