MM, SLT, RedIbis: I don't care very much about all those iron-rich microspheres, but anyway...
- When ordinary sheeple like we JREF debunkers see some evidence that some red-gray chips were found in WTC dust, we strongly tend to find an ordinary explanation for their origin: They are all very probably particles of some red paints, since such paints were
provably used in WTC (contrary to thermites).
- When we ordinary sheeple see some evidence that a significant portion of various microspheres (including iron rich) were found in the dust, we tend to find an ordinary explanation as well (following a wise principle of Occam's razor). The most probable/largest source of such spheres is apparently
a fly ash, frequently added to concrete for many decades,
which consists almost solely of such microspheres, including some iron-rich (see e.g. Wiki). The second most probable sources are WTC fires themselves, since such fires must produce some ash. Other sources (welding work etc) can also produce some minor portion of such round tiny things, namely those with a really high iron content.
There are perhaps tens of possible sources of such iron rich microspheres and even un-intended thermitic reaction might occur during WTC catastrophe in fire zones, e.g., reaction of hot aluminum with iron oxide in rust and/or primer paint containing iron oxide.
Unfortunately, there seems to be no direct proof that fly ash was used in lightweight concrete casted on WTC floors (apparently the most massive use of concrete in WTC). In my favorite NCSTAR 1-6b report (p. 21), there is a note that no record on the actual concrete mixture (its composition) was found. In the concrete mixture used for test floors, a kind of Haydite ("expanded shale, clay and slate") was applied by NIST (together with cement, sand and water), to attain similar density and mechanical properties (strength) as for original concrete.
Haydite, however, seems not to contain microspheres, but microcavities in the bulk material instead.
We simply don't know if fly ash was added to WTC floor concrete. Almond, who has a lot of experience in analyzing concrete, thinks, that fly ash was used for sure. Some others are not so sure. Anyway: if truthers want to seriously claim that microspheres can come mostly from the intended thermitic reaction, they first must exclude the possibility that they don't come from fly ash and other really probable sources. Good luck
, following ignition. If so, provide SEM and XEDS results as Jones/Harrit did for comparison with thier data. 
