Excerpt from Origin of the Iron Ores at Kiruna On the 'east side, the syenite passes with rapid transitions into the second phase, a syenite porphyry. Chemically the two phases are nearly identical; they are separated on the basis of difference in-texture. The phenocrysts of the porphyry are perthitic feldspars ranging from I mm. To 10 mm. In diameter. The ground-mass varies from that of a medium grained syenite to that. Of a rock dense to the naked eye. In no case has a glassy base been observed. Concretionary nodules of hornblende, apatite, magnetite, or biotite, and schliers of magnetite occur in the porphyry. Occasionally feldspar is found in these segregations. Some phases carry as much as 30 per cent. Of magnetite, by weight. The concretions are often surrounded by light-coloured aureoles or shells, suggesting that they 'have been differentiated from the mass in which they are en closed. About the Publisher Forgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.com This book is a reproduction of an important historical work. Forgotten Books uses state-of-the-art technology to digitally reconstruct the work, preserving the original format whilst repairing imperfections present in the aged copy. In rare cases, an imperfection in the original, such as a blemish or missing page, may be replicated in our edition. We do, however, repair the vast majority of imperfections successfully; any imperfections that remain are intentionally left to preserve the state of such historical works.