Day 25: Interesting Facts About Manganese
Atomic Symbol: Mn; Atomic Number: 25; Atomic Mass: 54.938

1. Take a deep breath and thank manganese. As an essential element in photosynthesis, without it, there would be no free oxygen on earth.
2. In our bodies themselves, there is only a tiny amount of manganese (10-20mg), which, comparatively, weighs less than a 100th of a dime! Yet, without manganese, we not only are unable to breathe, but we also could not perform vital metabolic functions.
3. Archeologists studying cave paintings that date back 30,000 years have discovered that not only did these early humans use manganese-based pigments, but they also used it as a cosmetic. In addition, the use of the element to remove green hues from glass was first implicated in the stone age, a technique that is still in use today.
4. Common uses include being used for drying black paints, preparing oxygen and chlorine, strengthening steel and other metals, gasoline additives, quantitative analysis, depolarizing dry cells, various medicines, and making colorless glass.

Image: Manganese is a silvery-gray metal resembling iron. It stimulates spontaneity.

Day 24: Interesting Facts About Chromium
Atomic Symbol: Cr; Atomic Number: 24; Atomic Mass: 51.9961

1. Many chromium compounds are distinctively colored, ranging from bright oranges and yellows to vivid greens and purples; hence why the name of the element is derived from the Greek word for color.
2. Chromium is the only element which shows antiferromagnetic ordering in its solid state at and below room temperature, although, when raised to a temperature above 38°C, the element becomes paramagnetic.
3. Chromium is commonly used to prepare pigments, in the coloring of rubies and gems, in some tanning processes, as a catalyst, and as a decorative and protective metal coating such as stainless steel.
4. As humans, we require trace amounts of trivalent chromium in our diets to regulate protein, fat, and carbohydrate metabolism. It also stimulates insulin activity, which means that future studies on chromium may provide insight into diabetes and how to best treat it. Chromium deficiency can result in poor control of blood sugar levels and diabetes-like symptoms.

Image: Chromium, remelted in a horizontal arc zone-refiner, showing large visible crystal grains.

Day 20: Interesting Facts About Calcium
Atomic Symbol: Ca; Atomic Number: 20; Atomic Mass: 40.078

1. Calcium plays an essential role in animal and plant nutrition, as it is part of many biochemical reactions such as forming skeletal systems, clotting blood, and controlling muscle performance. However, without enough of the hormones formed from Vitamin D, calcium cannot be absorbed by our intestines.
2. Yet, a balance in diet is necessary. Commonly reported side-effects of too little calcium intake include osteoporosis, muscle spasms, hypertension, numbness, depression, and irregular heartbeat; while side-effects of too much calcium include digestive problems, kidney stones, blood clots, fatigue, dehydration, and low blood pressure.
3. Calcium provides a significant link between the carbon cycle, climate and plate tectonics: when mountains are uplifted, calcium-based rocks and minerals are exposed to chemical weathering that releases calcium ions into surface water. Eventually, upon reaching the ocean, these ions react with dissolved CO₂ to form limestone, which then settles to the sea floor where it is incorporated into new rocks. 
4.  Common uses of the element include making cement and cheese, removing nonmetallic impurities from alloys, treating and purifying drinking water, and acting as a reduction agent in the preparation of other metals.

Image: Calcium grains, grain size about 1 mm.