Instantiated prefab doesn't collide with player

I am instantiating cubes on a mouse click, in order to allow the player to create a number of platforms for puzzle solving in game. The prefab they are associated with is Unity's standard cube with a texture and rigid body attached. However, while the prefab they are based on can be jumped on by the player and pushed, etc. the player falls through the instantiated cubes. Why is this?

Here is the script I have written:

public class ProjectileGeneratorScript : MonoBehaviour {

 public GameObject crystalCube;
 float nextSummon=0;
 public float summonRate = 0.5f;
 public float cubeSpeed = 10;
 public AudioClip summonFX;
 
 // Use this for initialization
 void Start () 
 {
 
 }
 
 // Update is called once per frame
 void Update () 
 {
     if(Input.GetButtonDown("Fire1") && (Time.time > nextSummon))
     {
         //print ("Bullet fired.");
         nextSummon = Time.time + summonRate;
         //Instantiate instance of projectile and cast to game object.
         GameObject cloneCube = (GameObject)Instantiate(crystalCube,transform.position,transform.rotation);
         cloneCube.rigidbody.velocity = transform.TransformDirection(new Vector3(0,0,cubeSpeed));
         Physics.IgnoreCollision(cloneCube.collider,transform.root.collider);
         //play fx
         //audio.PlayOneShot(summonFX);
     }
 }

}