安徽省绩溪黑云母二长花岗岩中高铁铁橄榄石大斑晶的研究

高铁铁橄揽石大斑晶产在安徽省绩溪县黑云母二长花岗岩中.岩石呈细粒花岗结构，矿物成分为条纹长石、更长石、石英和黑云母。大斑晶最大粒径可达5em，其中含有微小的磁铁矿自形晶，呈浸染状或断续脉状.在表生条件下，高铁铁橄榄石局部氧化成褐铁矿.大斑晶的外形、颜色和光泽等酷似黑钨矿. 大斑晶形成于上地慢高温高压条件下，先从花岗岩浆中结晶出铁橄榄石的高压变晶，岩浆沿深断裂向上部运移过程中，随着氧分压的增加而氧化成高铁铁橄榄石.

A study on Megaphenocrystsof Ferrifayalite from the biotite Monzonitic Granite in jixi,Anhui

Megaphenocrysts of ferrifayalite occur in biotite monzonitic granite in Jixi county, Anhui province. The rock shows finegrained granitic texture and consists of perthite, oligoclase. quartz and. biotite. The megaphenocrysts can reach 5cm in grain size, and contain small euhedral magnetite crystals in the form of dissemination or discontinuous veins. Under hypergene conditions, ferrifayalite has been partly converted into limonite through oxidation, and the megaphenocryst is quite similar to wolframite in shape, color and luster. The megaphenocrysts were formed in upper mantle under the condition of hightemperature and pressure. The high-pressure metacrysts of fayalite were first separated out from the granitic magma through crystallization; during the upward migration of magma along the deep fault, these metacrysts were oxidized into ferrifayalite with the increasing oxygen partial pressure.