It's about 200,000 times as heavy as a Penny.
In other words, 521 kilograms is 210,000 times the weight of a Penny, and the weight of a Penny is 0.00000480 times that amount.(United States) (formally one-cent coin) (Union shield design, 2010-present)
The weight of a United States penny is 0.0025 kilograms. According to a 2010 report by the United States Mint, the cost of manufacturing and distributing a penny is $0.0179 — more than its face-value.
It's about 300,000 times as heavy as a Playing Card.
In other words, 521 kilograms is 290,000 times the weight of a Playing Card, and the weight of a Playing Card is 0.00000340 times that amount.(ISO 216 B8 size, 2.5" x 3.5")
A single ISO 216 B8-size playing card weighs 0.0018 kilograms. Although this size is the most common home playing card, many casinos use "bridge size" cards — 2,640 sq. mm (4.036 sq. in) smaller in area.
It's about 350,000 times as heavy as a Paper Clip.
In other words, the weight of a Paper Clip is 0.00000270 times 521 kilograms.(average)
Notwithstanding the tremendous variation in sizes and materials, a typical paperclip weighs about 0.0014 kilograms. The country of Norway has used the paper clip as something of a national symbol since the end of World War II based on the erroneous notion that the paperclip was invented by a Norwegian, Johan Vaaler. However, the paperclip had already been in existence for at least 30 years by the time of Vaaler patented his paperclip design.
It's about 450,000 times as heavy as a Jelly Bean.
In other words, the weight of a Jelly Bean is 0.00000210 times 521 kilograms.(for Jelly Belly beans; approximate)
Made of sugar, corn syrup, and pectin, a single jelly bean weighs about 0.0011 kilograms. President Ronald Reagan cited jelly beans as his favorite candy and 3,200 kilograms of the candies were served at his first inauguration in 1981.
It's about 650,000 times as heavy as a Nail.
It's about 3,000,000 times as heavy as a Raindrop.
In other words, the weight of a Raindrop is 0.000000300 times 521 kilograms.(a.k.a. drop, a.k.a. droplet) (average)
The weight of a raindrop depends heavily on the type of weather, but averages about 0.0002 kilograms. The familiar teardrop shape of a raindrop is actually an optical illusion, caused by the reflection of the light and the motion of the drop.
It's about 20,000,000 times as heavy as a Grain of Rice.
In other words, 521 kilograms is 18,000,000 times the weight of a Grain of Rice, and the weight of a Grain of Rice is 0.0000000560 times that amount.(long grain; 14% moisture content)
A single long grain of rice weighs an average of 0.0000290 kilograms. A staple through most of human history, archaeological evidence indicates that the earliest rice cultivation was about 11,500 years ago.