To change the default Shape of a PointMark you can do this:
seriesDefinition.Appearance.PointMark.Shape = Telerik.Windows.Controls.Charting.MarkerShape.Diamond;
There is no PointShape
property in our Silverlight chart. There is such a property in our chart for asp.net ajax.
You can read about the features of the silverlight RadChart here
the Telerik team
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