JSON.NET serialization trouble

I have a class with property type of Point ( struct in .NET Framework). I use JsonConvert from Newton.Json to serialize it to JSON. But result is

 "Point" : "100,100" 

Instead of

 "Point" : { X: "100", Y: "100"}

When I replace JsonConvert with standard JavascriptSerializer, all works fine.

But I want to use JsonConverter from JSON.Net, because it's much faster.