avoid overlap problem when randomly instantiating

Hi , I wrote down a script to randomly put some Gems(Cubes) to my stage , I want to have 20 gems scattered , but sometimes they overlap . what's the best way to solve it . ( I dont want to destroy Overlapping Gems).

Here's my code :

 public class RandomPosition : MonoBehaviour {
      float rangeY = 3 ;
      float rangeX = 4 ;
      float y = 0.4f ;
      int count = 20 ;
      public GameObject gem ;
 
 
     void Start () {
 
         Vector3[] arr = new Vector3[count];  // random Position vector //
 
             for (int i=0 ; i < count ;i++)
             {
 
             arr[i] = new Vector3 (Random.Range (-rangeX,rangeX),y,Random.Range (-rangeY,rangeY)); // random Position vector //
 
             Instantiate (gem,arr[i],transform.rotation); // Creates random gems on Stage //
             }
     }
 
 }