Blakmax,
The pictures clearly show a structure using aluminium honeycomb core...What puzzles me is the insert in the earlier posting (#444?) which shows a carbon skin with a nomex core (not aluminium).
You see aluminum honeycomb core, I saw aramid paper honeycomb with phenolic resin, which is quite common for nacelles due to good resistance to temperature and lightning. It may be aluminum, better resolution would clarify...
In the images I attached in my previous post, I zoomed a possible lightning protection layer (if true then no doubt it's an aircraft debris) and a typical example of a carbon sandwich panel , carbon skins and aramid honeycomb core.
The picture below is a typical section of a nacelle panel (I do not know B777 sandwich composition),
reference
http://www.dexmet.com/1_pdf/LSP%20fo...20Aircraft.pdf
About size of this object, I estimate the object is measuring about 15in, any direction, based on the typical size of a cell of the honeycomb core of 1/8.
Cheers
Phoenix