That's rutin; weird looking, but perfectly safe to eat
If you’ve ever canned your own pickled asparagus, you may have been surprised at some point to find little crystals deposited along the spears.
These crystal formations are rutin, which is a pigment that occurs naturally in asparagus. Usually the crystals are yellow in color, but they could be gray or black if the water used for pickling had a high iron content. During the pickling process, the rutin compound, which is insoluble in vinegar, is drawn out and then crystalizes on the asparagus.
Rutin crystal deposits are harmless, and the pickles are safe to eat.
For further information, see these publications from WSU and the NCHFP:
Pickling Asparagus Information
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