What does the unit cell of petitjeanite look like?
Should one assume that the mineral petitjeanite and the chemical discussed in the recent Chemical &amp; Engineering News article Photocatalyst shreds drinking water contaminant PFOA are probably the same crystal configuration and unit cell, or can there be some variety?


No you cannot assume the structure from the formula, many materials have polymorphs (think graphite vs. diamond). To know if the structures are the same you must look at the diffraction pattern from the paper. In the paper the synthesized bismuth oxyhydroxyphosphate matches that of petitjeanite so in this case that is the prototype structure.



Using the information about diffraction, from the ICDD Databse (pdf 01-082-8058)we find that petitjeanite is a triclinic system of the $\mathrm P\bar 1$ space group (#2). with lattice parameters of: 

$\require{mediawiki-texvc}$
$$a = 9.798\AA; ~ b =  7.250\AA; ~ c= 6.866 \AA; \qquad \alpha = 88.280^\circ \beta = 115.270^\circ ~ \gamma = 110.700^\circ$$

and atomic positions of:
$$\begin{array}{c|lll}
\text{Atom}&amp;x&amp;y&amp;z\\
\hline
\ce{Bi}&amp;~~~0.52327&amp;~~~0.41421&amp;~~~0.7523\\
\ce{Bi}&amp;~~~0.29838&amp;~~~0.74044&amp;~~~0.55549\\
\ce{Bi}&amp;~~~0.07735&amp;~~~0.1609&amp;~~~0.28045\\
\ce{P}&amp;~~~0.6952&amp;~~~0.0172&amp;~~~0.9215\\
\ce{P}&amp;~~~0.0961&amp;~~~0.372&amp;~~~0.7862\\
\ce{O}&amp;~~~0.3777&amp;~~~0.5382&amp;~~~0.4759\\
\ce{O}&amp;~~~0.3066&amp;~~~0.1549&amp;~~~0.5579\\
\ce{O}&amp;~~~0.859&amp;~~~0.0275&amp;~~~0.8943\\
\ce{O}&amp;~~~0.5569&amp;-0.2084&amp;~~~0.8602\\
\ce{O}&amp;~~~0.621&amp;~~~0.1596&amp;~~~0.7526\\
\ce{O}&amp;~~~0.7684&amp;~~~0.1052&amp;~~~1.1811\\
\ce{O}&amp;~~~0.2584&amp;~~~0.5101&amp;~~~0.7497\\
\ce{O}&amp;-0.0468&amp;~~~0.4637&amp;~~~0.6902\\
\ce{O}&amp;~~~0.0209&amp;~~~0.1498&amp;~~~0.6362\\
\ce{O}&amp;~~~0.1695&amp;~~~0.3727&amp;~~~1.0506\\
\end{array}
$$

and last but not least this renders to an image of:



Purple: Bi
Orange: P
Red: O