Slate pencils are narrow sticks of soft stone or compressed material that were designed to write on slate boards. They were the standard writing tool for schoolchildren throughout the 1800s, before paper became affordable enough for everyday classroom use. Today, they’re mostly a historical curiosity in Western countries, but they remain widely available in parts of South Asia, where some people consume them as a snack, a practice tied to a condition called pica.
What Slate Pencils Are Made Of
Traditional slate pencils were carved from actual slate rock, a fine-grained stone formed when shale undergoes heat and pressure deep underground. Slate naturally splits into thin, elongated pieces along its layers, a property geologists call “pencil cleavage.” This made it easy to shape into writing sticks without much processing. The intersection of the rock’s natural bedding planes and internal fractures essentially pre-forms pencil-shaped rods, which is how the geological term got its name in the first place.
Not all slate pencils are pure slate, though. Many were made from soapstone (a soft, chalky mineral) or from compressed mixtures ofite clay andite stone dust. The pencils come in several colors. Gray and black varieties are typically closer to natural slate or shale. White versions contain moreite clay or calcium-based compounds. Red and brown pencils get their color from iron oxide content in the source material. The texture varies from gritty and hard to smooth and almost chalky, depending on the mineral composition.
How They Were Used in Schools
Before mass-produced paper became cheap in the mid-1800s, individual sheets were far too expensive for daily schoolwork. Students instead wrote on small handheld slate boards, roughly the size of a modern tablet. Slate pencils left visible marks on these boards, and the writing could be wiped clean with a damp cloth or sleeve, making the system endlessly reusable. A pastel rendering from 1822 titled “School Boy with Slate” shows this setup in action, and slate pencils from the 1880s survive in the Smithsonian’s collections.
The pencils had drawbacks. They produced a thin, scratchy line and made a sharp squeaking sound that anyone who’s heard nails on a chalkboard can imagine. Over time, soft chalk replaced slate pencils because it wrote more smoothly and quietly. Eventually, as paper prices dropped and public school systems grew, both slates and their pencils disappeared from Western classrooms entirely by the early 20th century.
Why Some People Eat Slate Pencils
If you searched for slate pencils, there’s a good chance you’ve seen videos or forum posts about people eating them. This is especially common in India, where slate pencils are still sold in shops and markets. People who eat them describe craving the earthy taste and the crunchy, chalky texture. Some compare the sensation to biting into a crisp mineral, almost like a very dry cookie made of stone.
This craving falls under pica, a condition defined as the persistent desire to eat non-food substances. Pica takes many forms: eating earth or clay (geophagy), raw starch, ice, chalk, or in this case, stone pencils. It’s more common during pregnancy and in people with nutritional deficiencies, though it also occurs as a standalone habit or compulsive behavior.
Health Risks of Eating Slate Pencils
Slate pencils are not food, and eating them regularly carries real risks. The most well-documented concern is the link between pica and nutrient deficiencies. A large meta-analysis found that people with pica behaviors had 2.4 times the odds of being anemic compared to people without pica. They also had significantly lower hemoglobin levels (the protein that carries oxygen in your blood) and lower zinc levels. Whether pica causes those deficiencies or results from them is still debated, but the two clearly feed each other: mineral cravings may signal a deficiency, and eating non-food items can block your body’s ability to absorb nutrients from actual food, making the deficiency worse.
Beyond nutritional problems, the physical effects of regularly chewing stone are straightforward. Slate pencils can wear down tooth enamel, chip teeth, and irritate the lining of the stomach and intestines. Some pencils, particularly cheap or unregulated ones, may contain traces of heavy metals or other contaminants from the quarry or manufacturing process. Over months or years, accumulation ofite silica dust oriteite calcium compounds in the digestive tract can contribute to constipation, abdominal pain, and in severe cases, intestinal blockages.
If you find yourself craving slate pencils or similar non-food items, it’s worth getting a blood test to check your iron and zinc levels. In many cases, correcting the underlying deficiency reduces or eliminates the craving on its own.