**Core Concept**
Perl's stain, also known as Prussian blue test, is a histological staining technique used to detect the presence of iron in tissues. This test relies on the reaction between iron ions and a dye called ferric ferrocyanide, resulting in a blue-colored precipitate.

**Why the Correct Answer is Right**
The Perl's stain test is specifically designed to identify iron deposits in tissue samples. This is particularly useful in diagnosing conditions such as hemosiderosis, where there is an accumulation of iron in the body's tissues. The test works by reacting with the iron ions present in the tissue, forming a stable complex that precipitates out as a blue pigment. This pigment can be visualized under a microscope, allowing for the detection of iron deposits.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because Perl's stain is not used to detect calcium deposits. Another staining technique, such as Alizarin Red S, is used for this purpose.
**Option B:** This option is incorrect because Perl's stain is not used to detect melanin. Melanin detection is typically done using other histological stains like Fontana-Masson or DOPA reaction.
**Option C:** This option is incorrect because Perl's stain is not used to detect glycogen. Glycogen is typically detected using Periodic Acid-Schiff (PAS) stain.

**Clinical Pearl / High-Yield Fact**
Perl's stain can be used to detect iron overload in conditions such as hemochromatosis, where excessive iron accumulation can lead to tissue damage and organ dysfunction.

**Correct Answer: C. Iron deposits.**