How do you create an Excel Gannt bar chart, where a date value will show an object?

I'm trying to create a automated excel gannt chart that runs off a pivot table from a SharePoint site. Is there any VBA coding or functions for excel 2013 where a date can represent an object (Such as a diamond) on the bars? I need to do this for a project mang request, where a diamond or shape would represent a commitment date.