Animate rock notes

Animate rock notes is a text by Robert the Strong that details his progress in making an Animate Rock Scroll to free Hannibus from his statue. Before he could solve a seer's riddle for the final ingredient, he was sidetracked by rumours of dragonkin and had to leave. It can be read in Robert's library by searching his desk in the middle though it cannot be obtained.

Transcript
I have found all parts of the incantation, the effective words of which are: 'Um nahi listic durooo-rah'. The ritual also requires two material components, the first of which is an emerald, but the second of which eludes me.

I went to a seer for this knowledge and - after I paid his price - he replied with this riddle:

'I feed upon the sword, spade and rake;

I pierce the armour that none can break;

One drop and I can stop a watch's flow,

But without time I cannot grow.

What am I?'

A rumour of a Dragonkin requires my attention. I will return to puzzle out the seer's riddle later.