The 60W weights 210g (charger + MagSafe 2 cable). Should be all right I guess?
Given the fact personal injury and death are legitimate concerns, don't guess. I'm sure you are aware that counterfeit power adapters are lighter because counterfeit product manufacturers omit a lot of safety-related components that are incorporated to prevent death or injury. However, a power adapter's overall mass is not very useful to identify a fake, nor is a cursory external inspection. Only a teardown could reveal the details, and that of course destroys the power adapter.
To directly answer your question you really can't use mass alone as a determining factor because Apple uses a variety of suppliers, all of whom may use different components that nevertheless conform to Apple's requirements.
Do the Wattage, Family, and Serial Number information in System Information > Power seem legitimate?
More importantly, is there a reason you would not want to purchase a power adapter directly from Apple or an authorized Apple reseller?