Armor Stands no longer appear when summoned holding an item.

I want to summon a armorstand holding a mini redstone block:
/summon ArmorStand ~ ~-0.23 ~ {Equipment:[0:{},1:{},2:{},3:{},4:{id:minecraft:redstone_block}],NoGravity:1b,Invisible:1b,Invulnerable:1b,Small:1b}

However the item or armor stand does not appear.