Did the 'goldish powder' have a smell? It may have been an herb. Garlic is commonly used for strength and/or protection. The marble I cannot say.Rice can be used in spells for blessing, money, prosperity, fertility, protection, wealth, security.
From the sound of it, it may have been for money. You don't know who could have left this?
The good news is I don't think it was of malicious intent!