Your use of the images of heat and fire and sparks is incredible... Your poem, for me, creates a very different idea/image of fire and warmth than what I usually associate those images with. And your use of gems in the third stanza is especially amazing... It is an especially great connection, as a ruby, most commonly associated with red and fire and passion, is the sought after gem rather than the sapphire, the (usually) blue and calming gem...
Your poem reads, to me, like a story might... Im not sure how to explain it... But the imagery you use speaks to me :)
I am familiar with the emotions and feelings that you present in this poem, but the way you portray them is beautiful :)
Well, you've pretty much put this 'feeling' in a nutshell. Well, a very thought out and poetic nutshell, that is.
The only real criticism I have to make is that here is only really one reference to the 'heart' and that is when it has been captured. But maybe you were trying to veer away from being like all the other poems and stuff by trying to not completely envelop the concept of 'heart.'
Also, to me, the last stanza feels like it could be followed up by something? Although, it seems cleverly done by referring back to the 'warmth within.'
Other than that, this is a piece which captures all those feelings and emotions really well.
Thanks for sharing :)