[blakestyger]

We used to see stuff very like this when I lived in Shropshire (UK). We thought it was either some sort of volcanic glass or slag from a smelting process.

[RD]

This at first glance reminded me of tar used in tarmac for roads.

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http://en.wikipedia.org/wiki/Obsidian

Snap ?

[Bass]

I would agree with RD that the black rock looks like obsidian- many of your other photos look like glass (whether natural or man made).  Can you provide descriptions of the rocks- how hard are they? where do you live? can you see any crystals in the rocks?  Do any of them break along fractures, or do they break like glass (no preferential planes of breakage)?  Are there any glass works or smelters about? 

Chert/jasper may be a possibility- looks like soft sediment deformation in several specimens. 

[avidgardener]

Sets 1,2,3,4,6,7,9,10,11,12,13 and 15 feel like glass as they make glass sound when tapped on a ceramic/glass surface. Sets 5,8 and 14 feel and sound like rock material. I live in England in the West Midlands, thanks RD for the Obsidian information hope this helps identify the others.

You might be correct blakestyger the material does resemble something spewed out of a furnace. As for the hardness its difficult to explain they were unearthed in the garden however the soil has way too many stones, pebbles and similar as above.