using System;

using System.IO;

using System.Text;

using Newtonsoft.Json;

public class Program

{

    public static void Main()

    {

        // Note: I'm using a MemoryStream here in place of a FileStream for demo purposes since I cannot write to a file on .Net Fiddle

        using (var stream = new MemoryStream())

        {

            using (TextWriter textWriter = new StreamWriter(stream, Encoding.UTF8))

            using (JsonWriter jsonWriter = new JsonTextWriter(textWriter))

            {

                JsonSerializer serializer = new JsonSerializer();

                serializer.Serialize(jsonWriter, new c());

            }       

            Console.WriteLine(Encoding.UTF8.GetString(stream.ToArray()));

        }

    }

    [JsonObject(MemberSerialization.OptIn)]

    public class c

    {

        public c()

        {

            x = 70;

            y = 36;

            z = 12;

        }

        [JsonProperty]

        public static double x { get; set; }

        [JsonProperty]

        public static double y { get; set; }

        [JsonProperty]

        public static double z { get; set; }

    }   

}