Kirkland in papers available on her web page argues that fine-grained hematite coatings might be a better match for the spectra in Meridiani than coarse grained hematite:

Laurel Kirkland
Infrared Remote Sensing of Mars and Earth
http://www.lpi.usra.edu/science/kirkland/

However, in her papers she states the origins of these coatings is not known in all cases. They might involve liquid water or they might not. One possible case where it's likely it does is when it is ferricrete, a type of duricrust which forms from precipitation from liquid water.
And Kirkland has noted that on Earth the formation of ferricrete often involves microbes:

Hematite on Mars: Investigations of a Terrestrial Desert Ferricrete Analogue
Frances Westall, Lunar and Planetary Institute, Houston TX 77058 and via Torino 10,
40139 Bologna, Italy.
Laurel Kirkland, Lunar and Planetary Institute, Houston TX 77058.
http://www.lpi.usra.edu/meetings/lpsc2002/pdf/1179.pdf

However, this ferricrete is normally reddish in color.

The fact that the hematite seemed to disappear when pressed down would support the hematite coating hypothesis, whether or not it involves liquid water. However, the (apparent) grey color of the hematite material at the Meridiani site would seem to support coarse grey hematite hypothesis, though Kirkland discusses a type of black hematite that is not coase grey hematite.

On her web site Kirkland also discusses other observations they might be relevant to the Meridiani site. She notes a very thin surface coating of dust or just a coarse surface can obscure mineral spectral identification. She has perviously argued this in regard to the lack of detection of carbonate deposits on Mars. This may indeed be the case with the bedrock observed at the Meridiani landing site. Observations by mini-TES on Opportunity have not found any identifiable minerals. Yet it has to be made of something as noted by mission scientists. Close up observations using the RAT tool may allow mineral detections to be made by looking under the surface.

Bob Clark