Have crystallized an organic compound and observed fine needles along with rombic crystals. The literature says that it crystallyzed in the ortho-rhombic crystal system and that when crystallizes it gives needles which grow along the dimension c. Can this be regarded as a sign hinting to polymorphism?
Polymorphism is not the only option. For example, simple ice crystallizes in form of needles or flakes depending on the conditions while atomic structure remains the same. Or you might have obtained some kind of solvate of the desired substance.
They may be polymorphs but as Alexander says above, they may not be. The same polymorph may, under certain conditions, have crystal growth promoted along different axes to give different looking crystals. The only way to know completely is to screen both kinds of crystal by x-ray diffraction to see if they have the same unit cell.
A different morphology does not necessarily imply a different crystal structure, as Joseph points out, though it may be a good hint to make worth a XRD screening. There is a wide literature on different polymorphs showing pretty much the same morphology, as well as the other way round. You might even find different polymorphs in the same crystallite, supposedly optically homogeneous at micrometric scale, a phenomenon sometimes called "phase mixing".
A distinct crystalline phase can appear in many habits for organic compounds which in general crystallize in lower symmetry crystal system. Further analysis such as SCXRD/ PXRD will be the best options to confirm the individual phase.
A distinct crystalline phase can appear in many habits for organic compounds which in general crystallize in lower symmetry crystal system. Further analysis such as SCXRD or PXRD will be the best options to confirm the individual phase.
Yes, they are concomitant polymorphs grown in the same crystallization batch. In this phenomenon the polymorphs may have variation in colors, morphologies, appearance etc.
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