Why can't I use Texture2D?

I’m trying to use a Texture2D with UnityGUI to create a button with an icon. However, Unity says that it can’t find the namespace for Texture2D. I looked up the namespace and it says it is UnityEngine which I am using I think:

using UnityEngine;

So what am I missing here? How do I use Texture2D? Here is my code:

using UnityEngine;
using System.Collections;

public class ButtonScript : MonoBehaviour {
	public Texture2d icon;
	// Use this for initialization
	void Start () {

	void OnGUI()
		if (GUI.Button (new Rect (10, 10, 10, 10), icon))
						Application.LoadLevel ("LevelSelectScreen");
	// Update is called once per frame
	void Update () {



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