Why is calcium harder than potassium?

How are hurricanes and typhoons created? How does the PTWC warn countries in the Pacific region about the possibility of a tsunami? What is the smallest unit of hereditary material found inside cells? What is earth's mass as a percent of Jupiter's mass? When does the time change take place in Canada eastern saving time? How have humans interacted with mars? Where is the exploding star in the solar system? What is outside the endodermis that develops vertical roots? What are the heaviest materials in the Earth found where are the lightest found? What is the coldest temperature ever recorded on planet venus? Does the pressure in the ocean change the shape of a glass bottle? Why can't you just have one map projection? How does stratification develop in sedimentary rocks? How many tbsp are in 4 cups? How does the structure of ethene compare to the structure of ethane? What two economies are important in most of Australia? What does it mean for a mineral to be abrasive? Which waves travel the fastest? What happens once a year but every day of the year? Which element contains the most protons radon sodium or copper?

Why is calcium harder than potassium?