“Migmatite,” meaning “mixed rock,” is a word coined in 1907 by Jakob Johannes Sederholm, for rocks having both igneous and metamorphic properties. Pierre Jardin stumbled on the term on a plaque for a large sinuous-striped, grey and white boulder named “Bob’s Rock” outside the Grassy Hollow Visitors Center on the marvelous Angeles Crest Highway near Wrightwood, California.
As Evelyn Mervine succinctly explains: “Metamorphic rocks are rocks which deform at very high pressures and temperatures and which may recrystallize but which have not formed through melting. Igneous rocks, on the other hand, are rocks which form by cooling from completely molten material. Migmatites are hybrid rocks: the dark layers (most often composed of biotite and amphibole) experienced metamorphic changes, but did not melt. The light layers (most often granitic in composition; as a reminder, granite consists of the minerals quartz, feldspar, and muscovite), on the other hand, crystallized from partial melts of the precursor rock.”
Pierre Jardin collected pieces of migmatite from an outcropping near Wrightwood. Their heterogeneous composition and pytgmatic foldings make them a natural fit for mixing rocks and wood in compositions Jardin calls “Igneous Ligneous Inosculations” (stones kissing stumps, loosely translated). The undulating folds of the migmatite rock rhyme visually with the sinuous lines of the wood, and the two forms fit neatly, creating nice negative spaces.