© Blackwell Publishing Ltd, Geology Today, Vol. 18, No. 5, September–October 2002200

BRANCH LINE

Branch lineOn the left you can see the join between two slabs

laid with their foliation parallel and dark streaksmatched as far as possible. In the lower right-handcorner of the picture the granite has a virtuallyundeformed igneous texture, well known to studentsin elementary petrology classes. The lightest patchesare crystals of feldspar 1–2 cm across; the light greypatches are quartz and the darker grey patches biotitemica. Between the undeformed granite and the darkheathen, deformation has imposed a foliation on thegranite, converting it into gneiss. The upper part ofthe picture also shows gneiss, somewhat less stronglydeformed. The larger feldspar phenocrysts have beenflattened into lens shapes, making this augen(eye-like) gneiss.

The heathen is darker than the granite, with ahigher proportion of mica and possibly amphibole. Itwas probably originally oval in cross-section and hasbeen flattened to a lens. Such enclosures were of morebasic magma than the granite, incorporated as aseparate liquid before crystallization. The large crystalof feldspar at the top of the heathen cuts across itssharp boundary, showing that it grew while the twocontrasting magmas were still fluid. The pattern ofthe cleavage cracks and the fractures of the crystalshow that, like the surrounding rock, it was flattenedby tectonic strain after the magmas had crystallized.Sharp-eyed readers will identify other magmatic andtectonic features.

I was so fascinated by the petrology lessons undermy feet that I missed a free drink of Coca-Cola andmost of the information given to our visiting group.But I put a bottle top to good use!

Coca-ColagraniteRoger Mason

Coca-Cola and associated drinks such as Sprite andFanta are supplied to Beijing and Tianjin from a fac-tory in the Beijing Development Area (BDA) about16 km SE of the centre of the city. The construction ofthe plant in 1997 was a major part of the growth ofthe BDA into a hi-tech satellite town separated fromBeijing by a green belt. The proximity of a motorwayto Tiarijin and the availability of abundant high-qual-ity groundwater from a well on site, drawn from aq-uifers below the sedimentary basin that underliesBeijing and the plain to the east and south, influencedthe choice of location.

When I visited the factory, the polished graniteslabs flooring the entrance lobby and viewing galler-ies above the preparation tanks and production linesimpressed me. Wang Qifa of the Chinese State Admin-istration of Foreign Expert Affairs kindly took the ac-companying photograph (Fig. 1) with a Coca-Colabottle cap scale, bearing the famous trademark in Chi-nese. Strictly speaking, the slabs are granitic gneiss –i.e. granite altered to a foliated structure by deforma-tion after it crystallized from its parent melt. Deforma-tion has gone far enough to produce a variety ofmetamorphic structures while retaining originalmagmatic features such as phenocrysts and enclo-sures (or ‘heathen’) of the kind that I usually study inkerbstones and paving stones.