Abstract
Northwest of Ottawa, near Otter Lake, Quebec, branching crystals of magnetite occur in gabbro dikes ranging in width from 60 m to 0.2 m, but highly complex dendrites (500 to 40 μm across) were found only in nine dikes, 2 to 0.2 m wide. Cooling rates in these small dikes are estimated at 0.6 to 60°C per hour. Complex dendrites are characterized by three intersecting primary plates (parallel to {100}), terminated by secondary arrowhead plates, bound by {111} planes. Many small projections have grown out from the primary plates, thereby isolating small cylindrical volumes of melt. Rare octahedra, ~ 20 μm across, and clusters of octahedra also are present. Ilmenite dendrites consist of two or more thin interconnected plates. Dendritic growth of magnetite and ilmenite is attributed to gradients of temperature, resulting from a large heat of crystallization, and of concentration in the melt about growing crystals, and to a tendency for the formation and persistence of {111} planes (magnetite) and {0001} planes (ilmenite).
Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
