Why might standard X-rays sometimes be insufficient for locating retained fine cactus spines during medical assessment?

Because the fine silica-based spines of some cacti do not show up clearly on standard X-rays.

While X-rays are a common diagnostic tool for locating foreign objects, their utility can be limited when dealing specifically with certain types of cactus spines. Many of the problematic, fine spines, particularly those from species like Opuntia, are composed significantly of silica—a mineral substance. Standard radiographic techniques rely on differential absorption of X-rays by tissues of varying densities, such as bone versus soft tissue. Fine silica-based structures may not provide enough contrast against the surrounding tissues to be clearly delineated on a routine X-ray image, meaning imaging techniques that detect softer materials might be needed.