AssetDatabase.IsNativeAsset

Description

Determines whether the Asset is a native Asset.

A native Asset is a file produced directly by Unity's serialization system (for example, a .mat Material file is a native Asset)

Note that scenes, prefabs and assembly definitions are not considered to be native assets.

Additional resources: AssetDatabase.IsForeignAsset.

using UnityEditor;
using UnityEngine;

public class AssetDatabaseExamples : MonoBehaviour
{
    [MenuItem("AssetDatabase/List All Native Files")]
    static void ListNativeFiles()
    {
        //List all native assets in the project
        foreach (var guid in AssetDatabase.FindAssets("", new []{"Assets"}))
        {
            var path = AssetDatabase.GUIDToAssetPath(guid);
            var asset = AssetDatabase.LoadMainAssetAtPath(path);
            if(AssetDatabase.IsNativeAsset(asset))
                Debug.Log(asset);
        }
    }
}